The March Roundup article Rolli referenced is a great start though in at least 2 spots, it makes choices based upon prices that don't exist now or, in some cases, even when the article came out. But w/o you giving us a resolution, it's hard to make a recommendation.
If no interest in DX11, the 250 is a great buy, usually available at < $100....w/ the free game it is a no brainer.
The 5770 works for DX11 well up to 1650 x 1050 but it's getting increasingly strained w/ each DX11 game that comes out.
Next up, the 470 looks very promising especially if you're into DX11 and high settings / AA / AAF. It has the lowest dollars per frame cost on DX11 games if the $350 MSRP actually holds ....given the performance, I think we'll see the 480 sit at MSRP but not the 470. The 5850 has gotten more attractive this weekend, as ATI has dropped the prices for fermi's release weekend.
AT the hi end, I find neither the 5870, 480 and especially the 5970 (at $725) very attractive at current prices.