Although I read not so long ago that AGP still has plenty of life left in it and we've barely expanded it's capabilities, by the way the market is going/being lead, PCI-E is the way to go. There will no doubt be AGP counterparts of the GeForce 7/Radeon X900, but they will probably be a lot more expensive.
EDIT:-
Counter-Strike said:
Thats funny w/ SLI. If you notice a 6600GT does better than 2x 6600GT's.
No, he means that according to the graph on Tom's hardware, one single 6600GT outperformed two 6600GTs in SLI, in the testing on Chronicles of Rid**** (by a frame or so)
The 6600GT outperformed the 6800 non-GT/Ultra, if that's what you were meaning.
Again, near the top of the chart, you can see that the single 6800GT outperformed two of the same card in SLI.
I know they haven't DJ-CHRIS, I just like to give you AGP users some hope . Since there are plenty of you AGPers out there, I can't see how it'll become obsolete just like that... Sorry, but the average person isn't going to want to upgrade their entire system just for PCI-E, not right now. It'd be bad buisness to outrule any future AGP cards.
EDIT: Oh, and I see now that a single 6600GT outperformed SLI'd 6600GT's in CoR, me bad. Must have been a dodgy Forceware install and/or a dud card ...
DJ-CHRIS: Just being sarcy man. Although you'd think Forceware would be efficient enough to effectively disable the second GPU in a case like this as opposed to loosing performance...