What you looking for is the PCI-Ex16 slot on the motherboard. That's what you should be looking for in type of graphics card. Here are a few from NewEgg.
A quick guide to selecting a gaming video card is looking at the memory of the card, and the gpu. For example: a video card with only 128 Mb of ram on the card, will have to pull lots of memory from the system. However a video card with 1 gig of ram or more will have to "borrow" less from the pc. Here is a good guide to buying a GPU for the best money from Tom's Hardware.