I was in the same position with a highend 775 CPU but was fortunate to get a hold of a nForce 790i board before they disappeared. Im afraid your best option at this point is grab one off Ebay, as any other S775 MB out in the market currently will be minimal quality and certainly not OC worthy for a great CPU and dual graphics support. In regards to dual graphics (assuming you go that route) remember X48 Intel boards will only do Crossfire (AMD) whereaas the nForce 680/780 and 790 boards are only SLI (Nvidia).
You won't bu stuck in that situation if you upgrade to the new architecture
I have a Intel DP45SG Extreme Series motherboard that takes DDR3 1333 memory but it is very picky about what kind of memory you use, I used kingston KVR1333D3N9K2/4G and it will handle a Q9650 with the latest BIOS update. I'm running a Q9450 with no problems. Your choice of motherboards is limited if you are running DDR3 memory.