depends on if you have some idea in building your own computer, I'm referring more on the side of desktop. If you want to build your own desktop then you can get like the six core AMD processor and high end graphics card to begin with.

There are some preconfigured desktops sold by HP, dell, lenovo that goes around $ 1,000 with the gaming config.

If laptop is your choice then go for the new ones with i7 processor with dedicated video card, with at least 4GB ram. My suggestion is you don't have to go with the $ 3,000 alienware while you can get comparable HP, Sony or even Toshiba Qosmio  for less than half of the price.