Id have said the same as above, get the GT 512MB, they are great apparently and better performace than a GTS of any kind, plus whenever you get a second one you'll be laughing(if you even need it)
I take it you have 22"+ screen? 2 8800GT's wouldnt be needed for a 20" really.
Also go for either EVGA,XFX or BFG, in order of preference