MOST people I speak with are ATI fans. I myself have an Nvidia GeForce III (ancient) but it has been absolutely reliable and I love it.
However, I am buying an ATI Radeon 9800 128mb card ($230) with my next computer and I think you probably should too. Either get the true ATI Radeon 9800, or the ATI Sapphire (ATI chipset n' stuff but made by Sapphire w/ better cooling) is about $20 cheaper and they're very popular.