I did a presentation in my communications class just this thursday. It was on installing a video card.
I explained why if you were to buy a video card today, you should go with AGP
1) It'll be like another year before your PCI-E card has to run at its max
2) 300 Bucks for a damn good top of the line video card (AGP), or 600 bucks for a mediocre PCI-E (still comparable though)
3) With the revisions AGP had, it's to be expected that PCI-E will have similar revisions and cards you buy today will be outdated (slot wise) in the future (so will agp, yet most people have AGP boards already, so no need to buy a new motherboard)
Of course if you want to have the power now, spend the money now, and now now now, then you should buy PCI-E cards...NOW