Bruce Mahler is rabbi Glickman (AKA rabbi Kirshbaum). He appears in 3 episodes: The Postponement (Season 7 Episode 2), The Serenity Now (Season 9 Episode 3) and The Finale (Season 9 Episode 24).
Bryan Cranston is Tim Whatley, the dentist who converted to judaism just for the jokes. He is in 5 episodes. The first: The Mom & Pop Store (Season 6 Episode 8)