I stumbled across Daughtry's cover of Lady Gaga's Pokerface and ended up spending too much time on Youtube looking for more decent covers. My favs:
Lady Gaga acoustic versionDaughtryGlee version with Idina Meznel and Lea MicheleAbsent Elk (British pop rock band)
Blowsight (Swedish alternative rock band?)
Glava's Trio (instrumental version with violin, bass, and some kind of percussive instrument)
You Me at Six (rock)
Two Door Cinema Club (electropop/indie rock band, doing acoustic with two guitars)
Pixie Lott (English singer-songwriter)
Marie from X-Factor France (she sang covers of a lot of good oldies, like "Ironic" by Alanis Morissette and "Don't Speak" by No Doubt, though I don't care for the way she sings)
The Internet once again manages to do the time suck thing. ^^;