Everyone is in it

The Muppets.

Mila Kunis, John Krasinski and Emily Blunt (d'aw), Ricky Gervais, Amy Adams, Jason Segal, Zach G...sadkjasdlkjsad-is, Neil Patrick Harris, Jack Black, Katy Perry, Rashida Jones (The Office), Selena Gomez, Whoopi Goldberg, Liza Minnelli, Billy Chystal and more and more.
Also, everyone is in Freaks and Geeks. I started watching all the episodes again (playing on IFC) and WOWEE-POWEE there are a whole lot of people who appeared on that show.