Good upgrade for what? Dual screens? 3D? Compute abilities? Gaming?
What is your budget? What is your current power supply? What is your motherboard model and name? What resolution do you plan on playing? What are you expecting from a new graphics card in terms of performance?
Quick question requires not so quick answer!
As far as budget goes. I'll spend up to 150 bucks. I forgot my motherboard and psu model. I no my modo is make by Asus and its socket 775. It has one pcie 16x slot. A budget mobo. And as for my psu. I forgot it was but I know it has 2 six pins connectors and one eight pin connector, and right now I game at 1080p with most details high and that's what I wanna keep doin. I just want faster frame rates now