from waht I remember:
8800 Ultra/GTX ----> 9800 GTX -----> 9800 GX2 ------> 280 GTX
8800 GTS 320/640 -----> 8800 GTS 512 ------> 260 GTX
As for the rest, I mean, their naming styles are soo different, I beleive the 8600 GTS was replaced by the 9500 GT.
The 8800 GT was a series on it's own, which was replaced by the 9800 GT ( same sh!)
8800 GSO replaced by the 9600 GSO
The 9600 GT I think just replaced the 8800 GTS 320 for the same power, but alot less of a price, these are just my estimates.
Remember just because they were replaced doesn't mean they are always better, I mean the 9800 GTX beats the 8800 ultra in somecases, and loses at higher resolutions and more AA from what I read.