Check it out.  It is about 45 minutes though all the way through (three episodes approximately 15 minutes each), so make sure you have the time to enjoy it.  But it's worth watching.

Dr. Horrible's Sing-Along Blog

Bah, I had the wrong link.  Now it goes to the official page.

Oh, and in case anyone needs any convincing, it stars Neil Patrick Harris.  And Nathan Fillion plays his nemesis.  And some guy named Joss Whedon was a writer and the producer.  Something to keep him busy during the writer's strike.

Man, that was just fantastic. Find the time to watch it, and it is closer to 40 minutes.

Thanks for the link!

-Doc