AnandTech: DFI nForce4: SLI and Ultra for Mad Overclockers. This is the new board to lust for. Did incredibly well and there is a mod that allows you to run dual cards at incredible performance...
even the bottom-of the-line Ultra-D to run 2 PCIe video cards in x16/x2 mode at about 90% the performance of full-blown SLI. Perhaps even more impressive is that a simple mod with a #2 pencil turns the Ultra-D into an SLI board, allowing any nVidia drivers to work in full x8/x8 SLI mode.
"Newegg":http://www.newegg.com/app/ViewProductDesc.asp?description=13-136-152&depa=0 has it right now for $169, so still expensive as it has just shipped. "Zipzoomfly":http://www.zipzoomfly.com/jsp/ProductDetail.jsp?ProductCode=246486 also has it for$165. This should slip back a little as availability improves.
"The Mod":http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=2322 seems pretty easy, you take a No.2 pencil and draw over two traces to connect them and then you have a \$40 more expensive SLI board.