Looking to upgrade my Graphics Card?

I am planning on upgrading my video card in a Gateway E4600. It has an AGP slot with a GeForce MX400 (64mb) in it right now. It has a 1.7ghz P4 processor and 512 mb of ram. What would be a decent graphics card upgrade for this system? I'd like to be able to play games with better frame rates than they are right now. I would not like to spend over $70 - $80 for this upgrade either. I am also planning on upgrading the PSU. A possible upgrade I was considering was a GeForce 6200. Please list some other options that would make a significant difference to frame rates from what I already have.