http://www.jibjab.com/great_sketch_experiment/video/shawshank
This. Is. Awesome. It's not roll-on-the-floor hilarious, but it's very well done.
It helps to have seen the film The Shawshank Redemption, which is one of the best movies I have ever seen.
Update: Morgan Freeman's voice in the video is great, right? Its done by Jim Meskimen who you might recognize as having been on the TV Sitcom, The Fresh Prince of Bel Air. Here is Jim doing another voice impression of Morgan. Pretty amazing.
Update 2: Oh, and be sure to check out the full list of Jim Meskimen voice impressions. This guy is amazing