I'd look for an X1600, they're around $100 these days. They're an excellent bargain with plenty of performance without spending money on cutting edge stuff.
I use one in my main system and just ran the demo of G3 without a hiccup, looked great. I'd look at the Asus silent one, which is what I got. No fan, just a BIG heatsink/pipe setup to keep it cool. For serious gamers planning to overclock it isn't a good choice but for out of the box use it's great. It also works quite nicely with 64bit windows systems, which is what I'm running on that system. That's nice for when you upgrade, since it will probably still be an upgrade for a standard 64 bit system.

Remy