Jeremy Piven
Appeared on: "The Pilot" (Season 4, Episode 22)
Role on "Seinfeld": Michael Barth, an actor auditioning for the part of George
Since "Seinfeld": Piven played Ari Gold on HBO's "Entourage" series and film. He was also the star of PBS's period drama "Mr Selfridge," which ended its four-season run in March.
James Spader? Really? Every heard of Pretty in Pink, or Less than Zero, etc etc...