If I were to buy a new graphics card out of those choiced above, I would pick the 6800GT. All those cards above will do a great job in terms of high fps and performance.
yeah bud, go with the 6800gt, best video card of the ones you listed.. however it does cost a little more than double of the 6600gt.. but there's double the pipelines.. if you have a pci express board.. defintiely get the 6800 gt
All would produce good settings, and if you have SLI, I'd get 1 6800GT if you can't afford two as yet, and then wheny you can afford it, get another one.
I wouldn't get a 6600GT if you can afford a 6800GT for example, only to want a 6800GT later on, as 2 6600GT's would probably equal (not exactly sure) 1 6800GT.
Hmm, I searched on net, and after my comment above, I'm starting to doubt that 2x 6600gt's will match 1x 6800GT because of SLI not meaning 2x the performance when used with 2 cards.
So yes, 1x 6800GT would probably still beat 2x 6600GT's in SLI.
They'd be quite a performance difference between the two I'm sure, though I've read the 6800GT is very overclockable, and more so than the Ultra is, if you like doing that.