@ id37878: The GTX260 and 1Gb HD4870 are both on Newegg for under $200.
I would not say one is better than the other and both are faster than the GTS250.
I would look for cards made by: XFX, EVGA and BFG, they have the best warranties.
Please tell us the make and model of your powersupply: It should be on a label on the unit itself, also the output on the +12v line or lines.