Here are my faves:
Joel Grey(Caberet)
Connie Stevens(love her rendition of "Teenager In Love"plus her duet with Kermit and Fozzie of "Close To You")(not to mention guest appearance by Ernie and Bert)
Avery Schrieber
Kaye Ballard(hilarious scene with Animal,as well as her battle with Miss Piggy)
Mummenschanz
Edger Bergen & Charlie McCarthy
Elton John(been a fan of his since childhood)
Julie Andrews(When You Were a Tadpole and I Was a Fish)
Peter Sellers(among my all time favourite comedians)
Leo Sayer(Miss Piggy's rivalry toward Annie Sue,love the way she jumped off of the dressing room corridor banister onto Kermit)
Gilda Radner
Harry Belafonte(love the episode's finale "Turn The World Around")
Leslie Uggams(special guest Big Bird)
Elke Sommer(Row Row Row)
Jean Stapleton(she got a little Edithy,if you know what I mean)
Cloris Leachmen(Kermit The Pig,Fozzie Pig)
Liza Minelli
Shields & Yarnell
Kenny Rogers
Crystal Gayle(the only time we saw Kermit without his collar)
Mark Hamill & Star Wars(another memorable episode finale)
Andy Williams
Alan Arkin
Carol Burnett
Loretta Swit(for once Miss Piggy got a taste of her own medicine)
Mac Davis(too many Beekers)
Paul Simon(cute duet of "50 Ways To Leave Your Lover" from Floyd and Janice)
Marty Feldman(SS muppets make guest appearance in episode's finale)