Here is one my my guitar heroes, Antoine Dufour, who covered Imogen Heap's Hide and Seek (that mmm whacha saay? song) on his guitar. Turns out he recorded it listening to the song, and someone put the cover over the original and they matched up almost perfectly, and I was surprised by how well they worked together. the cover on its own is a little boring and I could never stomach the original, but the guitar really fills out the sound left over by whatever she's doing with her voice.