The GTX 280 and 260 are the same line of nVidia cards, the 280 is better, comparable to the ATI 4870, but also costs more.
The 4850 (with a QX9650 @ 4ghz) gets 35fps @ 1680x1050 on all high setting, no AA.
I run the resolution a little lower and toss some AA in there, but AA in Crysis rapes cards, and favors nVidia (Crysis does, other games will see the 4850>gtx260 or equal)
Also - if you do want a graphics card, I'm selling my 4850, so you can pick it up for $105 shipped in the original box w/ original cords and all that. The lowest is $130 + shipping @ Newegg.