I love covers
First one that comes to mind is Jimi Hendrix' version of Dylan's All Along the Watchtower (and Hendrix' was probably the bigger hit, too)...then again I also like Michael Hedges' version of All Along the Watchtower a lot, but each are quite different. On the same album (Live on the Double Planet) Hedges also does a killer version of Prince's A Love Bizarre. Another that comes to mind is Los Lobos' version of Bertha on Deadicated (and on Deadicated are several very good covers of Grateful Dead standards).