www.drhorrible.com
Written and directed by Joss Whedon, and starring Neil Patrick (Doogie Howser) Harris as the mad scientist and Nathan (Cap'n Mal Reynolds) Fillion as the annoying super-hero who stands in his way. It's fairly standard Whedon material, but if you like his stuff (especially his singing stuff), it's a must-see. Hurry, though, because it's only online until July 20.
Personally, I can't wait for the sequel where Dr. Horrible visits beautiful Skullcrusher Mountain.