Billowing Black Robes: Snape shrine with OK fanart, some fun features.
Red Moon Rising: A Marauders' Site, includes slash, just to warn you in case you don't dig that kind of stuff.
Snape's Chambers: A good site, all Snape. Also looks at the wonderful Mr. Alan Rickman, who, as we know, plays Snape in film.
Tealin's Harry Potter Headquarters: Some interesting art and more.
The Chamber of Keys: Nice art, nominated for a Wingardium Award. Last I checked had some broken links though.
Fanfiction.net: Harry Potter and other fics abound here; I also recommend all would-be authors of fics read the column "S.P.I.W." by JK (whose surname isn't Rowling)