Kelly Perine is Usher in The Postponement (Season 7 Episode 2).
Ken Thorley is Vic the car salesman in The Mom and Pop Store (Season 6 - Episode 8).
Kevin Dunn is Joel Horneck, a childhood friend of Jerry's in Male Unbonding (Season 1 Episode 4).
Kevin McDonald is Steve (Denim Vest) in The Strike (Season 9 Episode 10).
Kevin Page is Stu Chermack in five episodes. The first The Pitch (Season 4 Episode 3).
Kyle T. Heffner is Gene, the bizarro George, in The Bizarro Jerry (Season 8 - Episode 3).
Larry David is the co-creator of Seinfeld, and Frank Costanza's lawyer in The Chinese Woman (Season 6 Episode 4).
Larry Hankin is Tom Pepper who played Kramer in Jerry pilot in The Pilot (Season 4 Episodes 23-24).
Larry Miller is the doorman who works at Mr. Pitt's apartment building in The Doorman (Season 6 Episode 18).
Lawrence A. Mandley is Larry, Monk's manager in 6 episodes. The first The Outing (Season 4 Episode 17).
Lee Arenberg is Mike Moffit in The Parking Space (Season 3 - Episode 21) and in The Susie (Season 8 - Episode 15).