The Breakfast At Tiffany's book club scene was hilarious because George made a reference to the movie what was completely different than the book.

The use of the same black family in the later episode one of many times the same characters would randomly appear in different episodes. Another one like that is the woman who goes braless, and who Seinfeld refers to as Elaine's Lex Luthor.
My favorite is the Johnny Cocharan like character who ends up getting a restraining order against Kramer.