What is your favorite cover song?
The best cover song I have ever heard belongs to Tori Amos. She has done a number of fantastic covers over the years, but my favorite was originally written by the Rolling Stones.
Several years ago, Amos released an EP of covers, "Crucify", including the song "Angie". Much as Groove Neuter said in his answer to the QotD, Amos manages to put her own, unique claim on classic songs without, in any way, pretending to be re-doing the original.