My Rat Infestation Deck has suffered few defeats, because it is simple, effective, and even if you can't get much land out, you can still cast creatures and make them grow!

Creatures

4 - Bog Rats (Yay Turn 1 creatures)
4 - Lab Rats (Turn 1 Creature, or buyback later in the game)
4 - Rabid Rats (-1/-1 to blocking creature)
4 - Razortooth Rat (Block THIS!)
4 - Dirty Wererat (Introduce a little muscle)
4 - Crypt Rat (Clear the board and finish almost ended games)
4 - Pestilence Rats (power equal to number of other rats in play.. uh-oh)

Artifacts

4 - Brass Heralds (Naming... Oh I dunno RAT!)

Instants

4 - Death Bombs (To get rid of unwanted opposition)
4 - Dark Ritual (Help get those Brass Heralds in Play)

Land

22 Swamp

Well the way I see it this deck is pretty self explanatory. You will run them down in just a few turns. Get as many rats out as you can! Your Pestilence Rats will be huge!!! Your other rats are no slouches either, even with just 1 Brass Herald in play. Don't be afraid to block and kill a few of your Rats, because there are plenty more rats where that came from. Even with only 3 land out, that's still a couple of rats a turn. Later in the game, use buyback on your Lab Rats and keep churning them out.. It even pumps up your Pestilence Rats. And when you're getting to the end and your opponent is finally starting to get into a position where he could hurt you, your crypt Rat has built in pestilence to destroy the weak... just finish him off. It will be a quick painful game... the best kind....