Dan Bull rapping about a sci-fi video game

A rock version of the Firefly theme by TheHumanTim

Darth Vader playing the accordion. Also a few piano players playing cellos

Deadpool vs Boba Fett, Epic Rap Battles of History

Incubus - Halo 2 - Follow

Mothership Connection

Chewbacca, Liquid Tension Experiment

MC Frontalot, Zero Day, about when the machines take over

Oingo Boingo, Weird Science

Need any others?