Kermit: Sam and Friends, 1955
Rowlf: Dog Chow commercials, 1962
Robin, Sweetums: The Frog Prince, 1972
Crazy Harry (ne Donald): The Muppet Valentine Show, 1974
Statler, Waldorf, Electric Mayhem, Sam Eagle, Swedish Chef: The Muppet Show: Sex and Violence, 1975
Miss Piggy: The Muppet Show, 1976 (developed from a puppet appearing in S&V)
Gonzo: TMS, 1976 (from a puppet appearing in The Great Santa Claus Switch, 1970)
Fozzie, Scooter, Bunsen: TMS, 1976
Beaker, Pigs in Space: TMS, 1977
Lew Zealand: TMS, 1978
Rizzo: TMS, c. 1979/80 (from a group of puppets appearing in The Muppet Musicians of Bremen, 1972)
Bobo: Developed from a group of bears in The Muppets Take Manhattan, 1984, one of whom had the Rowlf/Dr. Teeth style voice. Clearly a distinct character in Muppets Tonight, 1996
Bean: The Tale of the Bunny Picnic, 1986
Clifford: The Jim Henson Hour, 1989
Andy and Randy: Some fairy tale thing, 1990s
Pepe, Seymour, Johnny Fiama, Sal: Muppets Tonight, 1996
I think that covers the major characters.