I'd suggest at simple, not too expensive video card, like a Geforce 4 MX 400. But it really depends what you want to do with the computer. If you are heavily into games or high-end graphics, then you'll need a better video card than that.
But for basic game play, web surfing and general mucking about

, I find a GF4 MX 400 suits me fine.
Cheers
Mick