The 8800 GTX is now 1 full generation behind. (One full generation and one half-generation card set has launched.) It wouldn't surprise me at all if it quietly hit end of life quite some time ago.
You don't need a new motherboard if you are worried about PCIe v2. The v2 cards will work just fine on v1 boards. (Well, ok, there is like one in a bazillion which don't because they are on PCIe v1 instead of 1.1 which pretty much everything on the planet is, but still.)
Of course, if you have unlimited monies I'd recommend dual Evga GTX 285 Superclocked
$340 each post rebate. If you want to stick with a really good price to performance ratio and don't quite have unlimited monies, dual Evga GTX 260 Core 216 55nm
would be roxor at $245 each. Of course you'd need a 1920x1200 monitor to really push those. A single Evga 9800 GTX+
is likely the king of price-performance ratios right now, followed by a 9800 GT, but I'd really recommend for people looking at single GPU they look at the 9800 GTX+ or GTX 260 55nm.
(Of course this is all based on you wanting to pair an Nvidia card with an SLI motherboard.)
As Foz mentioned, I'd recommend trying to solve the 'why did they both die at the same time' issue before sticking new cards in there. If the motherboard or power supply fragged them it may happen with new cards as well. Have you tried disabling SLI and running just 1 card? Maybe only 1 is dead, but being set to SLI causes them both to fail.
As Foz mentioned, being BFG you should be able to send them in and get 'trade in value' towards new card(s) since they have lifetime coverage.
Oh bother... that means I'd need to convert all those reqs to BFG, good thing I basically have those at my site as well.
um... BFG GTX 285 OC
$360. They don't have a GTX 260 Core 216 in 55nm (for some reason Evga seems to be the only one I've seen so far). This GTX 260 Core 216
looks like the nearest match to Evga's at $260 post rebate. And here is a 9800 GTX+