If you wanted SLI with NVIDIA cards, you were stuck with Intel CPUs. I say were because this blog post by NVIDIA
has let loose that SLI is coming to AMD.
You'll want chipsets in the 990FX, 990X and 970 range that will have the possibility to support SLI in the initial batches and motherboards providers such as ASUS, Gigabyte, ASRock, and MSI will be ones that are bringing you this tech.
With that, I'm glad to see NVIDIA offering up more choices in CPU and motherboard for those wanting to run an SLI rig. Some might opt to spend a little less for an AMD setup and now they will have that ability of running multiple NVIDIA cards soon.