What's that Star Wars song called that was playing when the main character entered a bar in the first movie?
“Cantina Song” or alternative known as “Mad about me” was performed by the fictional band Figrin D'an and the Modal Nodes. The song was really created by John Williams, who was given direction from George Lucas who reportedly said: "Can you imagine several creatures in a future century finding some 1930s Benny Goodman swing band music in a time capsule or under a rock someplace — and how they might attempt to interpret it?" 

It was played it in Chalmun's Spaceport Cantina when Luke Skywalker and Obi-Wan Kenobi entered to find passage from Tatooine to Alderaan in Star Wars: Episode IV A New Hope.