BFG Tech BFGR88640GTSOC2E GeForce 8800GTS 640MB 320-bit GDDR3 PCI Express x16 HDCP Ready SLI Supported Video Card - Retail
The 512mb version is the better one believe it or not. Its a new release. THe older GTS, which I have, is the one you've picked
You shouldn't have a problem with 2 graphics cards fitting in a case nowadays.
Its certainly looking better now though! Get 2 of those GTS's and you'll be rocking as long as you are wary that 2 cards doesn't equal double the performance in most games.
I also believe early next year (2008), they are planning on releasing the 9000 series, which will drop the 8000 series down, and also create a new mid range winner in the 9000 series catorgory.