Well in a way it is not a single card, but who cares as this is a card you can plug into one slot and will give you the most frames per second for the money.
You can find these cards on the market but they are not that widely available as they are good sellers. The other Nvidia alternative is the good old 7900 GTX card that sells for around 400 these days, but at this price tag you also have ATI well performing and quietly cooled Radeon 1950 XTX.
I guess all Geforce 7950 GX2 cards will vanish before the big nasty G80 sees the light of the day. We believe that this week will be crucial for G80 details as Nvidia may start talking. µ