The Madeleine Kahn performance (yes, I know the post was '99 and you're not there any more!) was "I'm Tired", right? But the coolest musical moment still has to be Frankie Laine singing the title song.

I have 2 nominations:

In the biopic "Great Balls of Fire" the young Jerry Lee Lewis sneaks a peak in the window of a juke joint where a really fine blues singer played by Valerie Wellington tears the house down.   All the sweeter to see on film since the young lady has died since.

The end of the old Tom Skerritt/Pierce Brosnan film 'The Heist'-- at the culmination of an elaborate plan, Pierce gets to watch the ex-friend who framed him get framed himself trying to leave the country at the San Diego border stop with stolen stuff, while the Gipsy Kings sing "A Mi Manera", Pierce smiling in sweet revenge.

Anybody remember John Cullum breaking into song in Northern Exposure, was it at his wedding?