Neil Patrick Harris (you know, Doogie Houser)
Nathan Fillion ( Mal! )
Felicia Day (okay, you have to be a fan of The Guild to know that one...)
Simon Helberg (most recently Wolowitz on Big Bang Theory)
What do all these names mean?
An internet only musical cowritten by Whedon and featuring the talents of the above thespians. I'm really bummed I'm going to not be able to see the 3rd installment when it arrives. At any rate, check out the trailer and spread the word. Dr Horrible's Sing-Along Blog arrives on the 15th, 17th and 19th and won't be available after the 20th.
And check out the fan site.