During the recent writer's strike, Joss Whedon got together with a couple of friends and produced a short (approx. 40 min.) comedic musical starring Neil Patrick Harris, Felicia Day and Nathan Fillion. They made it on a shoestring budget, which forced them to get very creative. You can watch the whole thing here.

Dr. Horrible's Sing-A-Long Blog

Check it out. It's excellent.
_________________________
Your proposition may be good, but let's have one thing understood, whatever it is; I'm against it.