I always laugh when I think that Dalrymple’s 15 year old daughter was played by then 23 year old Denise Richards.
Of course she topped it herself when she became 17 year old girl from Wild Things being played by then 29 year old Denise Richards.
Catherine Keener was in an early episode as a artist girlfriend of Seinfeld. She was just starting her indie film career around the same time.
Her character stole lines from a Neil Simon play to break up with Jerry.
Lawrence Tierney’s character (Elaine’s father) never returned because the cast was afraid of him. Or so the DVD commentary said.
From the “I know way too much about this show” files:
Actually, I believe that she used the lines to keep Jerry from breaking up with her; she wrote him a letter, and it convinced him to keep seeing her. He broke up with her upon discovering that the lines were “borrowed.” 
I don’t recall the exact episode – I’m thinking it was the one where Jerry wrote a joke down in the middle of the night and then couldn’t read it in the morning – but there was a scene where he was watching a cheesy sci-fi movie on TV, and I’m pretty sure that’s Larry David on the TV.
Oh yeah, and wasn’t Rebecca DeMornay in the muffin top episode? 
Also voices Brock Samson on The Venture Bros.
Rob Schneider (Deuce Bigalow) played “Bob” in an episode. He had a hearing problem and Elaine went out on a date with him.
Dr Tim Whatley the dentist is played by Bryan Cranston who went on to become the dad in Malcolm in the Middle.