http://www.drhorrible.com/
I guarantee you this is the best sing-along blog you will ever watch.
It stars Neil Patrick Harris, Nathan Fillion and Felicia Day.
Made by Joss Whedon, or as he says "Aided only by everyone I had worked with, was related to or had ever met, I single-handedly created this unique little epic"
It was planned as a reaction to the Writer's strike, to get together and create new works that circumvented the system and was made specifically for the internet. It didn't get finished until after the writer's strike was over, but you can read all about that on the site if you so choose.
But I recommend you all check it out. A Supervillain musical? What's not to love?