Please fill in your system specs in the UserCP > Add System screen. Knowing what all components you have would help us make the best recommendation.
All things considered, personally, I agree with Balla. I think if you can find a GTX480 for $300, that is the best thing going right now at that price range for your resolution, assuming you don't mind having a somewhat noisy card. 6950 2GB is also a nice option, however you don't get the physX with AMD cards ... if you care about that sort of thing. Many people also feel that AMD doesn't do as good of a job with their drivers as nV, so you may want to consider that (although, this is, of course, a subject of constant, hot debate
Personally I generally
slightly prefer nV cards because of physX, the ease with which they OC and OV using Afterburner (no silly driver limits to work around like AMD sometimes has), the fact that they have individual settings profiles for each game built into the control panel (i.e. you can set 8xAA just for Bioshock, as an example), and that you can view your VRAM usage with nV cards, which you cannot w/AMD cards (at least, last I checked you couldn't, this may have changed as it's been almost a year since I rocked one).Edited by brettjv - 5/28/11 at 11:07am