Anything above what fer was telling you, you would need start at a 400w PSU to run gaming cards better than what was posted. Well you could get away with a GT 430 on a 300w PSU.
Then it depends on what size your CPU is as well. If you have to upgrade your PSU you want brands like Corsair, Antec, Seasonic, XFX, Silver Stone, and some brands of OCZ.
Good luck to you and get back to us with what your are thinking about.http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107-7.html