any 8600 is basically the equivalent of the 7600, except it's directx10. you can get an 8800gts 320mb for only $260, only going over your budget by a few bucks. but that's only becuase of the $20 rebate, so it's really $280.
i would go for the 8800gts. it's EVGA. everyone seems to have an 8800 now. you don't really need the 640mb version of any card if you don't run at higher resolutions.
evga 8800gts 320mb
edit: nevermind, the card went up to $270 after a $20 rebate. i've been watching it for a while, it stayed at $260 for quite some time.