I am buying a new tower, and I want to get a good gaming tower, what should I look for?

I'm not looking for anything special, I just want a good computer that can run programs like World of Warcraft and Starcraft 2 on good graphics, and be able to run it fast without lag spikes. Im looking for around 600 bucks max for just the tower. I dont want to build my own, but what sort of video cards/ram should I look for in stores?