Entertainment....Thy name is Amplitude
Not only does it have a good mix of music by popular artists (Slipknot, P.O.D., Garbage, Quarashi, and RUN DMC to name a few), but it is addictive as hell. Not only that, but you can create your own tracks and beats, as well as take it online.
I am usually not a fan of music based games (Like Parappa the Rappa? Ick.), but this is one for the ages. Everyone has those "I'll sell my grandma's meds before I depart with this" games in their collection. This is one of mine. Sorry, Grams.
-B