Jack Black is an actor with one big presence in Hollywood. When he's on screen, you want to watch him. That's why it's so surprising that I still find movies that I didn't know he was in. With his comic success, especially with his band Tenacious D, it's easy to forget he started as a serious actor.
In some of his older, lesser known roles, you can see Jack Black laying on a thick Southern accent in 'Dead Man Walking,' getting his arm blown off in 'The Jackyl,' playing Matthew Broderick's friend in 'The Cable Guy,' and standing in a few frames of 'Demolition Man.' If you don't mind violence, I suggest checking out his final scene in 'The Jackyl.' It's gruesome, but it really shows him acting very well while still having that signature Jack Black style.