The boys from Boyce Avenue perform some amazing acoustic covers of pop songs. Same with Hannah Trigwell, who has collaborated with them a couple of times. Their covers of Passenger's "Let Her Go" and Coldplay's "The Scientist" put the originals to shame, IMO.

One of my favorite covers of all time is Relient K's cover of "Sloop John B".

I don't care what you think of Country music, Kenny Chesney absolutely nails his cover of Bruce Springsteen's "I'm On Fire".

Greg Laswell's rearrangement/cover of Cyndi Lauper's "Girls Just Wanna Have Fun" was so good Fox flat-out stole it for an episode of Glee without bothering to credit Laswell for it. Great job, Fox...

While it's kind of a cliche at this point, I think we can all agree Johnny Cash's cover of "Hurt" by Nine Inch Nails just demolishes the original.

If you've somehow missed Disturbed's rendition of the Simon & Garfunkel standard, "Sound of Silence", I feel sorry for you. Goosebumps every damn time, man.

I could go on and on, but I think that's enough for one comment. :)