What is a good affordable gaming computer?

So, im trying to get into gaming on the pc, and i would like to get a gaming pc that i can play games such as MMO like WoW. and fps like mw2. but im not sure what my rig should include, and i have only a little bit of room to wiggle with the budget, up to 3000, and i was wonder if theres any advice on cpu. video cards, etc., oh and if theres any websites like alienware, and ibuypower.com where you can customize it to your own personal taste.