This dunk is too often overrated as one of the best dunks ever, but it is extremely impressive nonetheless. Nance easily skies to the basket over 7'2" Kareem Abdul-Jabbar, one of the greatest shot-blockers in NBA history, making the dunk even sweeter.
This arrangement of dunks is the only footage available, but the dunk I'm talking about starts at about the 0:15 mark.
Nance was one of the first NBA big men to put down vicious slams, and his dunks have been re-used by many other players since his time. In addition to being one of the best Phoenix Suns players in franchise history, Nance is most famous for participating in the 1984 Slam Dunk Contest, where his one-handed cradle and windmill dunks stole the show.
Nance won that day despite going up against legends like Dominique Wilkins, Julius Erving and Clyde Drexler, among others. Nance's athletic dunking ability also earned him the nickname "The High-Ayatolla of Slamola".