With that resolution and processor, I would personally recommend an ati 4770. A very cool and efficient card (built on some of the technology utilized in the new 5xxx series from ati released in the past week or so) and it has been shown to punch above its weight as far as performance is concerned.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150369
I always recommend XFX for the industry leading double lifetime warranty (be sure to register the card!) as it increases resale value, second hand buyer will also get a lifetime warrantly. Also XFX uses reference coolers, which exist the heat out the back of the case.
Don't bother with the extra cost of the 1gb version. At your resolution 512mb will perform excellently. The extra cost might gain a few FPS here and there, but would only show a marked increase in performance at 1920x1080 or higher resolutions.
If you are intent on staying with Nvidia, the a GTS250 512mb is also a good choice for your price range, though perhaps overpowered for your processor, and your PSU. If you are using a no-name brand of powersupply, then be wary, as they won't be as efficient or honest with their ratings as a brands like Corsair, Antec or Seasonic. There are other great brands of PSU, but those are just the first that came to mind.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150357
Again, I linked to XFX for the same above reasons.