Well, you obviously need an SLI board. You basically have 1 big choice:
-650, 680, or P35 chipset?
650 and 680 are mature, P35 is brand new. Up to you. That being said, 650 is cheaper, 680 is more expensive but better features. P35 is most expensive.
Suggestions:
-MSI P6N (650)
-EVGA (680)
-ASUS P5N32-SLI Plus (650/680 hybrid)
-Gigabyte P35 board....pick one that works for SLI
P35 won't do 8800 SLI (& it's probably the middle 1 in terms of price).
With 2 x8800GTX you really ought to go 680i for the dual x16 (650i does dual x8).
The new DFI 680i LT looks interesting & from the cs pov eVGA are probably the best (there are a no. of different eVga revisions though so you ought to research the differences more).
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