Seinfeldian Guest Stars

Well, since it's been over three weeks (a fortnight and a half, really) since a new post has been added here, I thought I'd try and get something going.

I was watching Seinfeld earlier tonight in syndication and was struck by a thought I'd had several times before. I think one of the hidden gems that made this show so good was the quality of the guest starring actors on various episodes. My first example if Bookman, the library investigations officer from the episode where Jerry finds out he forgot to return a book he took out in 1971. His scenes are a bit overdone, perhaps, but the actor just continues to run with it, even to the point where Jerry can't keep a straight face. Pure comic brilliance.

Anyone else?