How about Barbara Streisand showing up on "Coffee Talk" in SNL? I'm getting VERCLEMPT just thinking about it.
Although the BEST CAMEO EVER was Dennis Hooper giving Christopher Walken a history lesson on Scillians in "rue Romance".
One more...Reese Witherspoon flashing a picture of her father (Richard Speck) in "Freeway"--blink and you'll miss that one.
Also from SNL...Barbra Streisand crashing CoffeeTalk with (Mike Myers; Madonna and Roseanne Barr); and one of the best skits ever...Christopher Walken "I need more cowbell!!!"