Hi,
The king of these is, of course ... Manfred Mann and his Earth Band. Started with "Mighty Quinn", and later "Blinded by the Light", and later yet, "Singing the Dolphin Through" and all of these really excellent versions. But we all know that Jimi's Watchtower is the boss of all versions of any song!
Best?
I like 3 or 4 versions of "Season of the Witch", and specially the "Masked Marauders"
The Doors' version of Whiskey Bar should have given everyone a reason to do some Kurt Weill on stage ... instead it killed it. Beautifully though! Not sure that most rock audiences have any idea of this connection, though.
The Clams' "Close to You" is actually better and more fun to listen to than the original.
Guru Guru made Bo Diddley and Chuck Berry sound bad and cheap, which they were.
Steve Hackett can do Genesis way better than they did ... of course, they quit doing it, which did not help!
Stevie Ray Vaughn had a few dandies ... and his version of several of these were excellent.
Frankie Goes to Hollywood ... The War song ... absolutely nothing ... is awesome.