8800GT, 9800GT, 8800GTS, 8800GTX, 9800GTX, 8800Ultra, 9800GTX+, GTS250.
That's just my shot in the dark. 8800GT and 9800GT have identical specs and perform pretty much the same. the GTS is a rebadged 9800GTX+, the 8800Ultra is an OCed 8800GTX, and the when comparing the 9800GTX with the 8800GTX, you have to remember that the 8800GTX has 768MB of ram which does help it beat t he 9800 in some benchmarks at high res, but overall it's more of a tossup between the two.
Nvidia hasn't been very good with their naming schemes lately. In terms of performance to numbers I'd say ATI has it better. This is of course taken with a grain of salt since ATI is starting to clutter their lineup with cards of similar or disproportionate performance (like the rumored 800SP 4830)