Some great pop covers mentioned in this thread ... Vision Divine's "Take on Me", Avalon's "Kyrie".
You can't go wrong with Blind Guardian's gover of the Chordettes' "Mr. Sandman" or Squealer's remake of "Enjoy the Silence" by Depeche Mode (I suppose that's not exactly pop). Sonata Arctica's "Wind Beneath My Wings" is probably one my favorite covers ever.
However, I think the pop cover that takes the cake is Lemur Voice's version of "Beat It". Those beatnickey jazzy breaks they effortlessly injected ... brilliant.