Despite the Master Plan's statement that the online videos would be shut down on July 20...

Dr. Horrible's Sing-Along Blog

...Acts 1, 2, and 3 are still viewable (and extremely entertaining) online. My only caveat is that it is sort-a-kind-a PG-13, but just barely. If you are a Joss Whedon fan who missed his latest production and first web-production, wander over to the site linked above.

You can find more info at the Official Fan Site.