I like to play this game with Kris.

She has this thing with remembering lyrics (if she has heard a song twice, she knows every lyric). I have been finding weird song covers on Tumblr. I quiz her to name either the person singing or the name of the song. She gets it about 80% of the time.

Examples:
Ben Gibbard covering Thriller
The Kooks - Young Folks (Peter Björn and John cover)
Kids by Ben Lee originally by MGMT
Frankmusik / Such Great Heights
Franz Ferdinand - Call Me by (Blondie Cover)

and probably the best cover I have found to date:
Hot Chip & Peter Gabriel - Cape Cod Kwassa Kwassa (Vampire Weekend Cover)