'Nique, of course, was the best. Dr. J was close (still could dunk at 63 years old). David Thompson deserves to be in this discussion. Kemp, Griffiths and quite a few others here could match up with Carter.
But I'm throwing out another name I haven't seen here - Larry Nance. The 6'10" dude could easily hit his head on the rim when he went up. I've never seen a guy get as high as he did and he could bring it down with authoritah. The High-Ayatolla of Slamola defeated Dr. J (albeit an aging one) at the first slam dunk contest.