I bet you already know all about these sites, but just in case... Also, just in case: the link order follows the importance of these sites for review-addicted people - of course, based on my opinions. Where do I place my site, you'll say? Hmm. Please decide for yourselves!
First of all, here is a great site for you that explains the whole meaning of life!
Second, here's a great site to go to if you feel a desperate need to flame me but ready to flame somebody else instead, if only it'll help you vent your frustration.
And now, on to some serious stuff:

On the plus side:

1. This is where you'll find a terrific lot of reviews for more than 90 bands - everything from The Monkees to Slayer. Mark is the real eclecticist, unlike me who's only pretending to be one (but I'm trying to do my best anyway) - he digs everything from sissy folk to hardcore punk and is able to distinguish between good and bad in every genre (except maybe blues rock which he seems to have a bone to pick with), even if what's good to him may not always seem good to you, and vice versa.
2. There's interactivity - lots of comments already posted and still more awaited from you. Sometimes it's even more interesting to read the actual comments than the reviews (no offense). Of course, comments also include flames from assheads. Let's hope you are not one. If you think this is a minor problem, go check his Ballbreaker review on the AC/DC page; it is already a classic piece of interactive writing in its own rights and deserves to be framed, in case somebody finds a frame that's huge enough.
3. Users are sometimes invited to write their own reviews - if they're active and persistent. I was. At this point, I believe, there are already more user-written reviews there than Mark's own: he's kinda busy with other things, so people write reviews for him. Heh. And poor Rich Bunnell has to moderate it all.
4. Needless to say, the reviews are mostly fascinating, funny and quite intelligent, even though the writing style is sometimes a bit obscene (you won't have any problem with that if you like Zappa's Joe's Garage, though). I've never laughed so much throughout all of my Web seances. He's a great writer!
5. Hey! I also wrote some reviews for him! And posted my comments! Actually, I reviewed Jethro Tull, Cream, Lennon and McCartney. But these are not the same reviews as here, so calm down. They're probably more funny, but they're also a bit more stupid; I was a know-nothing amateurish beginner back then.

On the minus side:

1. Too few bands from my beloved 60's - too many punk, alternative and metal. But well, somebody has to review all that stuff, doesn't he? I suppose there aren't too many snobs like myself on this sad little planet of ours...
2. Like I said, the style is sometimes offensive, but you can always vent your frustration by sending hatemail. Anyway, if you're a diehard, any style will seem offensive to you. And Mark will post everything, no matter what you say about him. He's such a nice guy.

On the plus side:

1. This is a HUGE review site (and, believe me, when I say huge, I mean heaps and heaps and heaps of info) covering hundreds of bands and artists. These guys really have a vast knowledge, and I wish I could equal them someday... then again, who wants to be a soulless encyclopaedist? :)
2. The site is run by two really intelligent dudes, though sometimes a bit snobby. Really. It's no problem for them to put down a serious artist as if he weren't worthy to lick their boots. And they do it mercilessly. But they're always honest, and their defiant anti-commercial stand makes them something like the Worthy Knights of Reviewing in the business (gee, even Prindle had put up a link to CDNow at one time, and I guess I'll end up doing the same. Gimme gimme gimme).
3. The site also has lots of interesting features, like Top 20 lists, etc. You can also find lots of useful technical information that I, for one, have been to lazy to incorporate in my reviews. They always check out and give out detailed band line-ups, information on session and guest musicians, etc., sometimes including albums they haven't heard yet. It's also a great place to look up an artist's entire discography.
4. If you're attentive enough, you'll find a brief overview of rock'n'roll history - for novices and experts alike. A bit hard to find, though; start from the main page.

On the minus side:

1. The worst defect, of course, is that there's no interactivity: no comments posted, no outside reviews allowed. Which is unbearable - what can you do if they put down your favourite record? Put your fist through the screen? They say they don't reply to hatemail, but I'm pretty sure they receive tons of it. Thankfully, I have resisted the temptation (although, gngngngn, I hate it when people put down Quadrophenia or Selling England By The Pound).
2. Most of the reviews are rather short, not always giving an accurate picture of the album. This is probably the worst defect. I can understand them - they have such a lot of records, after all. But sometimes you really can't figure out what the record is all about. I wish they'd be less formulaic and dry. This certainly works as recommendations for the new-buyers; but serious analysis this often ain't. Then again, maybe they're just not going for it. It's all right, anyway.
3. Their main principle of acquiring records is: if it ain't cheap, it ain't worth it. Of course, it's understood that if they didn't buy all these records cheap, they'd either have to limit their reviewing space or have to engage in stock exchanging, but now that they have acquired every good record that was found cheap, they don't have any choice but to stick to inferior material. I mean, they've only added a dozen or so really interesting records over the past year, unless, of course, it's really interesting for you to check out all those obscure Latin bands or the Riot Grrl stuff or all the hip-hop material.

On the plus side:

1. Here is where you'll find solid, intelligent reviews of lots of 80's bands - punk, alternative, pop, etc. Burks is a good specialist in all of these genres, the newer the better. Apart from that, he also reviews movies and has some other cool stuff; be sure to look it up.
2. Unlike Wilson & Alroy, Brian was also trying to be democratic and his site was fully interactive - until he dumped it and went off to Taiwan, that is. He's since got around to updating it again, but at a slower pace.

On the minus side:

1. There are rather few 'classic' bands (in my understanding) - Beatles, Beach Boys, Kinks, Who form a minority, together with lesser-known proto-punk stuff like the Stooges and MC5. Quite unlike me, Burks doesn't consider the Sixties the 'golden age' of rock, preferring to concentrate on the power pop and proto-punk bands. And when he goes about, like, completely closing his eyes on prog rock bands that, want it or not, represented one of the leading directions in music around the early Seventies, this is where I have a major bone to pick with him.
2. VERY offensive style - in places. Burks seems to waste no chance to dump art rock into the trashbin, and on almost every page there's some pun or offense hinted at Pink Floyd or Yes or somebody like that. Oh well. I do the same thing for punk. I guess we are even. On the other hand, we're both fans of the Kinks and Roxy Music. In this respect, it's better to notice similarities than differences.

On the plus side:

1. Not quite 'anonymous', actually - the site is run by Nick Karn (who sometimes actively comments on my site, as well) and his pal Casey Brennan. The site is extremely well-organized, with some of the most comfortable and intelligent design I've seen in a long time.
2. The reviews are informative and never offensive, written in a critically correct, but rarely boring tone. While the opinions expressed there are certainly subjective, they are also cool-headed and well thought out. Extremely nice.
3. As usual, the site comes with the now customary gadgets, like interactivity. They also invite contributors to write reviews, so take your chance while it's still there!

On the minus side:

1. While the site is formally 'band-oriented', the gaps in discographies are often so huge that it's in reality 'album-oriented'. More or less solid pages have only been finished for a few classic rock bands like the Beatles, although I can't really say anything about Nick's reviews of various heavy metal bands, as I'm not an expert in this matter and don't know if he has all the albums by, say, Queensryche, or not. Even so, the site structure never seems clumsy or 'gapped' due to the design.
2. Too much emphasis on the heavy metal side for MY tastes; I know Nick's main area of expertise lies there, but that don't really comfort me. But, like I said, the reviews are intelligent, and if you're a civilized, not a braindead, metalhead, this should probably be the first and best place to visit.

On the plus side:

1. John takes his work seriously - he really wants his site to look solid. The reviews are long but not boring, the amount of technical information is just about right, and it's obvious he does a lot of listening and analysing. Good work.
2. Interactive. (As if this surprises anybody these days!)

On the minus side:

1. Again, the site is quite young, but it's growing more rapidly than quite a lot of other record review sites. It's suitable to vist it something like every three days or so - you're sure to find yet another album reviewed.
2. It's just my personal opinion; I don't think John has yet entirely found his style. I see a lot of influence there - mainly from Mark Prindle (naturally) and me (surprise surprise - I already influence people!). But it's just influence, and he's developing rapidly. On the other hand, maybe I just think so because our tastes coincide close to perfectly: we both rate Led Zeppelin as the band's best effort, and we both think Who Are You is underrated. This is good! Taste coincidence is an incredibly important thing in this world: it shows a way to finding an objective solution to art.

On the plus side:

1. Another good ol' funny site - Ben is a good, devoted and completely unpretentious music fan whose opinions are well worth checking out. Also, if you think I have highly underrated Neil Young, this is the first place to go from here for some relaxation.
2. Ben, like Bryan, is yet another humble guy (even if in this case self-humiliation sometimes comes close to being obnoxious; sorry, Ben - you gotta trust in yourself a little more). Anyway, it's so soothing to find somebody who's not opinionated beyond hope of repair, like me...

On the minus side:

1. A very new site - just about twenty or so albums reviewed - but Ben may not update it unless he's encouraged by visitors, so do him a favour! It'll grow anyway. Right now, he seems more preoccupied with his online journal (which is also fun and worth reading; Ben does have quite a lot of writing talents).

And here are some lesser sites for you:

Classic Albums (site status: moderately active): run by Paul, this one concentrates more on separate, usually well-known albums, tackling classics from different genres (from AC/DC to U2 to the Stones to whatever), and can serve as a good introduction for the rock'n'roll freshman.
The Internet Homepage Of Pope John Paul George Ringo The Second (site status: unknown): run by Tommy Joice, more of a poet and amateur-philosopher than a musical critic, it does feature some interesting attempts at music reviewing.
Rock Is Dead - Long Live Rock (site status: moderately active): run by Marco Ursi, not too fast on updates, but well-crafted and heck, the rate of updating always depends on the readers, so go and read it.
Too Much Time On My Hands (site status: active): run by Martin Teller, a bit too over-emotional for my tastes, but due to interactivity, a good place to drop a load as well.
The WOSPS Music Review Archive (site status: moderately active): run by two mega-pretentious dudes, it's mostly dedicated to Eighties/Nineties stuff.

Greatest & Worst Songs Radio Playlist: not exactly a review site, but a very important and thought-provoking site in any case. Run by Mike O'Hara, it tells us of the fascinating American plots to ban British music from the airwaves, and the author certainly has something going on there, although everything he says must certainly be taken cum grano salis. (Warning: site currently down).

Genre-dedicated sites:

Prog.net: a good source for user-written reviews of all kinds of prog- and art-rock. Only recommended for progheads, of course, as records often seem to be praised exclusively on the basis of how many "prog" elements they actually contain (song length, complexity, etc.). Which is only natural anyway.
Satan Stole My Teddybear: an enormous site with entertaining reviews, concentrating on heavy metal and hardcore for the most part. Not a favourite of mine, understandably, but their style is very respectable.

And, of course, if you can't find your particular review anywhere on these sites, you're sure to find it at:

The All-Music Guide: their reviews are often skimpy and biased, and it often seems to me that their ratings and their reviews have nothing to do with each other (they rate all of the albums, including those that they'd never heard), but it's a good spot to look for some factual information, and hey, I stole most of the album covers from there.
Amazon.com: the "ultra-subjective factor" rules supreme here, but it's a good spot to look for all kinds of different opinions here anyway. Just don't make the mistake of buying a record according to somebody's recommendations on there.