The GTX 260 is a bit more expensive than the 9800GTX, but they perform much better. The ones to look for are the core 216 versions. They can be had for as low as $154 after rebate: GTX 260 core 216
Another card that performs better than the 9800GTX is the GTS 250
. They are available as low as $105 after rebate.
What are you looking for in a CPU and motherboard? AMD or Intel?