Agree with islandstate however have to point out that if the card you use is not SLI ready and you have an SLI motherboard then you can't just add another card in when you want to upgrade the graphics, if you want to then use the SLI you will need to buy 2 new cards.
Any Graphics card you buy will have to be of PCI-e design.
If your going to be only using 1 Graphics card then any PCI-e card will do. But it will work out better if you just get an SLI-ready card and use that. You will then have the option of adding a further card later on if you wish.