Building a computer. What parts should I get for this?

[Lemur]

This looks tailor-made for you: How to Build an Awesome Gaming PC for $647

Note that $105 of that is for Windows—if you have student access you can cut that down to $65 in the USA, even less elsewhere. And if you already have a legitimate copy of Windows, you can cut that to $0, bringing the cost of the build to $542. (I'd use the savings to move up to a slightly beefier videocard.)

-edit-

I don't understand the ATI hate in this thread. Yes, there are problems with ATI cards, and we all have to wait for a patch/fix. Are you suggesting that this simply does not ever happen with Nvidia cards? Bugs and patches are a feature of modern PC gaming. Driver problems are not unique to any company, and if anything, Nvidia has a richer and more epic history of such problems. If you can't stand that, best to consider moving over to a console.