For SLI, you're going to want to find a recent-model nVidia chipset motherboard, due to the fact that only nVidia makes SLI cards.
Basically, you'll want a recent model AM3 or AM3+ (more upgradeable in the future) board. AM3+ I believe supports AM3 CPUs, though you'll want to check up on that to make sure.
If you go to nvidia's website (http://www.nvidia.com/
) you can find information on their recently released chipsets, including what they support.
You'll want to go with something supporting 740a, 750a, 780a, or 980a SLI chipsets, according to their site, and you'll want an AM3 motherboard not an AM2+ as that will work with DDR3.