srv - little wing
zeppelin - gallow's pole
crossroads - cream
a lot of good covers have been played by phish as well. (great gig in the sky, while my guitar gently weeps, freebird)
There are way more really bad covers out there than good ones. One that comes to mind that really pisses me off is korn's another brick in the wall. I can not put into words how much i hate that "band". . .

A lot of dylan songs have been redone, most of them not very well. Tambourine man was pretty good by the byrds though. big yellow taxi was horrible by the counting crows. Knockin on heaven's door is pretty good by guns n roses.