A Voodoo3 if you want dead cheap.
A GF2MX is the best bang for the buck, but more expensive than the V3.
I love my V3, nice 2D image quality, 55-60FPS in quake3 in HQ settings (ok it's 16bit with a 22bit post filter, not 32bit, but the rest of the settings are HQ). Gives me an 800x600x32x85Hz desktop with good 2D, and I've never had any driver issues or game compatiblity problems with it.