I game at 1680x1050.
I have a GTX 260 and it does its job well, but in some of the 'hardcore' graphical games (Metro 2033, Crysis, etc) it can slow down at times.
If I had to choose today and only had a budget of up to $350, I would go with a GTX 470. You can get one for as little as $350 and even cheaper with sales.
At any rate, I would probably not invest in a single GTX 200 series (260, 275, 285, 295) at this point any more unless you plan to SLI because they don't have DX11, and they don't have the performance of the newer cards (5850, 5870, GTX 400 series).
If you can find a couple of GTX 260 cards for ~$175, I would get two of them and SLI.
/opinion