It really depends what he's going to run and how much money he has. I bought an ASUS Geforce 6200 128MB for $53 (AGP card because this system is without a PCI-E slot), and it runs quake 2 and counter-strike: source quite well, is stable, and text is sharp (I've had cheap cards which displayed blurry text). I never have slow downs in quake 2 with this card. I occasionally have my framerate in CSS drop to about 40 fps in areas with tons of people shooting in one area (like in fy_iceworld), but usually it's around 40-70fps.
The specs are not all the same on 7900 GS's either.
[quote author=j