I'm not going to link to Avril Lavigne's cover of the one Nickelback song I know becauzzzzzzzz. Instead, here's an inspired performance by Yoko Ono, singing Katy Perry's "Firework" (thanks to the magic of sound editing).
(Oops! Kelly O posted this video on Slog over an hour ago. Sorry for the double dose of crazy Yoko mash-ups. Anyway, go vote in her poll!)