First off is Count Basie and Frank Sinatra being musical together in 1965.
Paul Newman serenading Louis Armstrong and Duke Ellington in Paris, 1960.
Carrie Fisher and Harrison Ford acting casual.
Here's Fred Astaire being Fred Astaire, with Bing Crosby giving him some tips.
And here we have Edith Piaf and Django Reinhardt doing a little palm reading in Paris in the 1940s. Look at that great neckscarf he's wearing!
(photos collected from awesomepeoplehangingouttogether)