Till now it was the 8800GTX card which was the best in the market, but now it seems that there is another competetor for this monster, its the 8800Ultra.
This new monstrous card is heavily priced at $829.

The 8800 ultra version includes premium versions of the GTX’s components, overclocked to a 612MHz core clock, 1500MHz shader clock and 1080MHz memory clock.

Even though this card is heavily priced, it just beats the performance of 8800GTX by an increase of about 10%-15% only, which is too less for this heavy price tag. According to me if one has a 8800GTX, then its not worthy to be dumped for a 8800 Ultra. Same applies for a SLI setup of the 8800GTX cards as well.