I made a poll like this a while back when deciding. Based on recommendations i got the gf 3 ti 200. You'll be able to clock it to near-TI 500 performance levels.
Unlike the GF 4 MX the gf3 has full DX8 support. John carmack says doom will run better on GF3 ti 200. That's about all you need to hear.
<< When I have a
problem on an Nvidia, I assume that it is my fault. With anyone else's
drivers, I assume it is their fault. This has turned out correct almost all
the time. >>
hehe