There's Statler & Waldorf, Bunsen & Beaker, Kermit & Piggy, Kermit & Fozzie, Gonzo & Rizzo, Johnny & Sal, Seymour & Pepe, Rowlf & Fozzie, Floyd & Janice, Sweetums & Robin, Gonzo & Camilla and many other combinations.
The recent Fozzie and Kermit interviews have made me think about this more...