6. Jack Black
Jack Black has made us laugh in plenty of movies, including High Fidelity, Shallow Hal, and even just with his voice in Kung Fu Panda. His most musical role was in School of Rock in which he played a slacker with a love of rock and roll who impersonated his roommate to make some cash as a substitute teacher, and ended up forming a band with his students. He actually earned an Academy Award nomination for the role for Best Actor in a Musical or Comedy. In addition to his acting career, Jack Black formed a rock comedy band with his friend Kyle Gass, releasing three albums under the name Tenacious D. They definitely have cred in the rock world since Dave Grohl has played drums for each of their studio albums.