The Bruisers cover of Billy Joel's Lunatic, or their cover of Fortune's Son.
Vital Remains cover of Judas Priest's 'You've got another thing coming' was also sensational, but, I wouldn't put it ahead of the original...just because hey...it's Judas Priest.
Gang Green's original 'Alcohol' was great (Screw you Brad Paisley), but Tesco Vee and the Meatmen did a pretty awesome cover of it.
Also, John Blackburn and Karl Suessdorf's 1944 'Moonlight in Vermont' (first vocalized by Margaret Whiting), was covered many many times afterwards, and the list of better versions is pretty large, Chet Baker, Tony Bennett, Ray Charles, Nat King Cole, Stan Getz, Dizzy Gillespie, Billy Holliday, and my absolute favorite of the bunch Ella Fitzgerald and Louis Armstrong.
