"Airplane" ... 'I am serious ... And don't call me Shirley!'
"Some Like It Hot" with Tony Curtis, Jack Lemmon, Marilyn Monroe - movies are just not made like that anymore.

Either the BBC or the Drew Carey version of "Whose Line Is It Anyway"
DVD or VHS of the Carol Burnett show, especially any scene in which Tim Conway and/or Harvey Korman are trying not to laugh.