A single GTX 470 is good for gaming right now and for the next year or two at least. It's roughly between the HD 5850 and HD 5870 in gaming power.
If your video and image editing software is CUDA enabled a GTX 470 would get you some GPU acceleration for those programs.
You can overclock a 470 yourself. After market type custom coolers usually follow the reference model cards a few months later if it looks like there is a demand for them.
Your motherboard should have the SLI bridge in the accessory pack since not all motherboards have the PCI-e x16 slots set up the same distance apart.
but some board malefactors are going to come out with non stock solutions, i saw a pic somewhere that has 3 92mm fans i believe, something like that, so in a few months they're be out, but nvidia has really done a pretty good job with it's heatsink this time around to coup with the heat issues
Wish I could choose more then one best answer. Everyone helped very much. The reason I was asking about SLI is that some where I read that it has better scaling than crossfire, which I guess means it uses more of the second card.
Does anyone know any new AMD boards? The FX series that could handle SLI?
SLI and Crossfire both scale similarly, there are some games where SLI does better and others where crossfire does better, they are pretty much equivilent.
The only boards that support SLI are X58 and P55 chipsets for intel CPUs, there are no good AMD boards that support SLI, there are some with nVidia chipsets but those have not earned themselves a good reputation.
If you are considering an AMD build, go for an ATI card, the 5850 performs similarly to the GTX 470, uses less power, and costs less. You might want to price out an intel build that supports SLI with a GTX 470 and an AMD build with a 5850 just to see if there is a significant difference.