Here are Newegg's dual 771 motherboards with two PCIx16 slots:
http://www.newegg.com/Product/Productco...72%2CN82E16813131170%2CN82E16813131152
However, note that the second PCI"x16" slots on most of these are 8X or 4x; also, no nVidia SLI, and, from what I can tell, no Crossfire on these. Only nVidia makes SLI capable chipsets, and from what I can tell, they do not make a socket/dual socket 771 version.
There are some dual socket F/AMD Opteron socket 1207 motherboards with SLI:
http://www.newegg.com/Product/Productco...38%2CN82E16813182114%2CN82E16813131140
This board looks good for SLI/dual Opterons:
http://www.newegg.com/Product/ProductReview.aspx?Item=N82E16813131141
Intel Xeons are great, but, if you want SLI in a dual processor workstation motherboard, you may be limited to the Opteron option.
Lots of socket 775 SLI boards:
http://www.newegg.com/Product/Productco...11%2CN82E16813127022%2CN82E16813141002
Lots of AM2 SLI boards:
http://www.newegg.com/Product/Productco...04%2CN82E16813136020%2CN82E16813188016
Here is AMD's "4 x 4" program board--not sure what software you are running and if you need 4 cores, but this will do it, and also do SLI:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131146
The prices on the CPUs that go with it are not too bad:
http://www.newegg.com/Product/ProductLi...343+1051727346&name=Socket+F+(1207+FX)
(I think those are them....I thought they only came in pairs, can't tell from the description if that is what they are....and, I can't find it on AMD's web site....)
4 x 4 motherboard review:
http://www.dailytech.com/article.aspx?newsid=4963
Hi res image:
http://content.zdnet.com/2347-12554_22-38068-38069.html?seq=1
With the dual 8800 need you have, I would assume this is to be a gaming machine?
Depending on what software you are planning on running, a single socket quad core (looks like there are some nice ones coming soon) might work well for you too....
HTH,
NXIL