You're playing Crysis with your current setup? Wow ...
Anyway, for that budget you can get (in order of decreasing performance) - a 4850, 9800GT, 5670, GT240, or 4670. All are capable of light to "medium" gaming. For reference, I had an 8800GT (same as the 9800GT) and Crysis was playable on high settings, 1440x900 resolution, with an E8200.
Hope this helps.