Christa Miller fired George in the Sniffing Accountant for feeling her material. She played a woman in The Doodle who didn't care what George looked like.
Marty Rackham was Jake Jarmel and also I believe he played a cop in The Trip, Part 2 when Kramer was suspected of being a serial killer.
Patrika Darbo was the woman who wouldn't get up so George could slip his boss a mickey. In The Snifffing Accountant Newman felt her material and she screamed. Newman panicked and ran off. Although, technically she could have been playing the same character.]
Christine Dunford was the performance artist who threw chocolate on George and he tried for revenge at her baby shower. Also played the salesbitch who didn't want to tell Elaine about the Mannequin.
The most famous example was Suzanne(?) Snyder played a nazi and also was Poppie's daughter.