Note:  These have not been updated for 6th Edition except for the Vampire Counts at this point.  Ravening Hordes don't count!
Bretonnia
My Bretonnian army is built around a solid contingent of Knights of the Realm.  With a 75% character allowance it is easy to "cheese out" with these guys, but I've won well enough without doing so.  I've even avoided using the more powerful orders of knighthood for that very reason.  The result is, I believe, a rather well balanced force.  This is the only army in which I've included a Battle Standard Bearer.  With a human army, I feel that is essential!
Barony of Loch Lomond
Chaos Dwarfs
Two sample Chaos Dwarf armies are detailed elsewhere so no link will be provided below.  I feel the CD's are an incredibly balanced force, and it is a shame they have been discontinued.  I build my army around a solid block of CD infantry and Black Orc slaves.  The Bull Centaurs and wolf riders harass the enemy while the arty punds away. With a character mounted on one of the CD's unique flying beasts, these guys are rock solid.

Instead of an army list, how 'bout a FAQ?
WH FAQ, 5th Edition
Chaos-Beastmen
By far one of the least powerful armies (IMHO), the Beastmen are still one of my favorites.  The Children of Chaos are very colorful on fluff, and any who can get a hold of the old 3rd edition Chaos books should get them for the background.  A solid block of Gor are hard to beat, with my general present and a champion to accept challenges.  The chariots are a more vital part of this army than any other
Baphomet's Beasts
Chaos-Warrior
Like my Chaos Space Marines, this army is based around a Nurgle theme.  Why?  Because its fun, that's why!  Who can resist a character named Fartulance?  I used to call the army Fatulance's Flatulators before I decided to use a Hero for a general.  Chaos troops are horribly expensive, and thus small.  I've tried to mitigate this not using much Chaos armor.  After all, how many rank-and-file would have it, as opposed to champions? This also makes the army a bit slower, rather fitting for Papa Nurgle, but powerful nonetheless.
The Green Machine
Lizardmen
Here is my first army.  I one the campaign at my local hobby store with an army of these guys (league record of 7-1-1).  The Saurus troops can go toe to cloven hoof with anyone, and the skinks are versatile in many ways, despite dying in droves.  The monsters which flush out the army make up for a "lack" of war machines.  My Stegadon named Sparky the Thunder Beast is a living legend in local circles.  The stories in the army book are among the best fluff in a long time.  This is one army wher the death of the general won't cause much panic (3d6 on leadership tests is hard to beat).
The Gecko Gods
Undead
I'm not entirely thrilled with the way things have been broken up sice the original Undead book, but I can understand their reasoning.  The armies do have a distinctive falvor now, one Egyptian and the other more Gothic.  Khemri is a "faster" army, with light chariots and more cavalry on the average.  The Vampire Counts tend to be more shambling and a near Chaos rip-off as far as the Bloodline abilities are concerned.
Tomb Kings of Khemri
Vampire Counts
Wood Elfs
The Wood Elfs make a nice change from several of my other armies.  Very shooty, but kind of suck in hand to hand combat.  You can't have too many archer types here!  A small unit of Wardancers and Glade Riders do provide some close combat ability, however.  Float like a butterfly and sting like a bee is the motto (where have I heard that?)
Asatru Kindred