In 2007, Harris worked with Mike Nelson on an audio commentary for RiffTrax. The two "riffed" on the film "Willy Wonka & the Chocolate Factory". Harris is a big fan of the cult TV series Nelson worked on, "Mystery Science Theater 3000". Harris was interviewed for a 1992 Comedy Central special "This Is MST3K" hosted by Penn Jillette about the series and its fans. In 2008, Harris played the title role in Joss Whedon's musical web series "Dr. Horrible's Sing-Along Blog" alongside Nathan Fillion and Felicia Day. The first episode of the series debuted on July 15, 2008. He has also provided his voice for the Disney California Adventure Park attraction California Screamin'.