I made a thread about this a while ago, and I ran into the problem of having a weak PSU. This time around, I have a 750w Corsair PSU, and I have another 200 dollars for a GPU, rather 175 so I can get it delivered before I leave for college. What I'm thinking getting is in the thread name.
I agree with fiduke. I do not think dismissing power and heat concerns for pure performance is a good idea.
There are rumors of some gold-plated GTX480s that may have been forged by Hephaestus, but I think you'd be better served by either a HD7850, or if that is too expensive, a GTX560Ti.
Edit: Assuming your budget allows, I would choose HD7850 > GTX560Ti > HD6870. I like XFX or HIS for AMD cards, and MSI or EVGA for nVidia. Asus makes great mobos, but I've had trouble with probably half the Asus GPUs I've bought.