First question before suggesting anything... what are you going to be doing?

Unless you do a lot of gaming, anything by Nvidia and ATI is going to be a waste. Get a Matrox G550 ($125 or less). It doesn't have great 3d... about on part with a GeForce 2.... but the regular Windows performance and quality is years beyond anything nvidia and ati has.

If you do a lot of gaming... I'd go with something by Nvidia, I've used a couple on other peoples systems and have built a couple systems for people with them. I've never had good times with ATI cards/drivers.

Which one? Which ever one is the highest your willing to spend. You get what you pay for. More money, more speed, more options.