Anyone who’s interested in the Muppets should check out Kermitage, a web site which lists every character, every episode of the Muppet Show, and (soon) every piece of Muppet merchandise and memorabilia ever created.
Did you know that the guy in Mahna Mahna (from the first episode of the first season) was performed by Jim Henson? And the two pink cow-like creatures, called Snowths, were performed by Frank Oz (with one in each hand, I presume).