When George Lucas was mixing the American Graffiti soundtrack, he numbered the reels of film starting with an R and numbered the dialog starting with a D. Sound designer Walter Murch asked George for Reel 2, Dialog 2 by saying "R2D2". George liked the way that sounded so much he integrated that into Star Wars.
The scene in which Luke and Leia swing across a shaft in the Death Star was filmed in one take. The stunt itself was performed by Mark Hamill and Carrie Fisher.
In the bar on Tattooine (where Luke and Obi-Wan meet Han Solo), you see lots of aliens at the bar. Look carefully in the background of these shots, and you'll see a NASA astronaut in full space walk gear (helmet etc) walking across the back of the shot, complete with American flag on his arm. It's quite obvious once you know where to look.
James Earl Jones' name did not originally appear in the ending credits. At the time of the film's release, Jones felt he hadn't done enough for the film to deserve a credit. His name was added for the film's re-release.
George Lucas decided to release "Star Wars" in May 1977 instead of the start of the summer movie season (in the 1970s, it was a new concept as the result of the success of "Jaws" in 1975) in June because he wanted kids still in school to talk about it so as to spread word-of-mouth.
The name of the planet Tatooine came from the town of Tataouine in Tunisia where the movie was filmed.
During Han's conversation with Greedo, the line "Even I get boarded sometimes - do you think I had a choice?" was lifted from his conversation with Jabba that didn't make it into the original release. If you pay attention you'll notice that when he says that line the camera is on his hand cocking his gun, not on his face. When the Jabba scene was put into the Special Edition they left the line in both scenes, which is why the Jabba scene seems a bit repetitive.
The film's screen tests were spoofed in a 1997 episode of "Saturday Night Live," which included Kevin Spacey playing Christopher Walken auditioning for the role of Han Solo. Walken really was considered for that role before Harrison Ford was chosen. Spacey also played Walter Matthau auditioning for Obi-Wan Kenobi and Jack Lemmon auditioning for Chewbacca.
The reason why C-3P0 lets R2-D2 go in front of him as they enter the Skywalker's residence right after being purchased from the Jawas, is because the set guy operating R2-D2 by radio control kept on hitting C-3P0 from behind and pushing him down the stairs, so in the final shot, C-3P0 suddenly steps to the side, waves R2-D2 past, and the shot cuts out right before R2-D2 goes flying down the stairs.