Ian Patrick Williams is Stubs in The Wink (Season 7 Episode 4).
J. Patrick McCormack is Mr. Leland in The Bizarro Jerry (Season 8 - Episode 3).
Jack McGee is Ralph, a highway maintenance worker, in The Pothole (Season 8 Episode 16).
Jack Plotnick is the crew leader of Sushine Carpet Cleaners in The Checks (Season 8 Episode 7).
James Hong is Bruce, is the restaurant manager in The Chinese Restaurant (Season 2 Episode 11).
James Karen is Mr. Canterman in The Puerto Rican Day (Season 9 - Episode 20).
James Lashly is Russian Cable Guy in The Baby Shower (Season 2 Episode 10).
James Lesure is a Kramer's co-worker at Brandt-Leland in The Bizarro Jerry (Season 5 Episode 11).
James Pickens is Detective Hudson in The Finale (Season 9 - Episodes 23 and 24).
James Rebhorn is District Attorney Hoyt in The Finale (Season 9 - Episode 22).
Jason Alexander is George Costanza in all Seinfeld episodes except The Pen (Season 3 Episode 3).