Just thought this needed its own thread since it started hogging another. Having listened to George Lucas explain it, the story is largely a mix of traditional myths and legends with the style of action designed to be like old adventure films and serials with the spaceship action designed to be like dogfights from WWII films.
Personally, I think the strongest similarity is to the legends of King Arthur.
Luke (like Arthur) is hidden away as a child by a wizard and later mentored by him. Of course he didn't have to pull the sword out of the stone, but a light saber is close enough to Excalibur. He even has a thing with his sister (Morgan Le Fay is Arthurs half-sister). Of course Darth Vader gets the uniquie distinction of being his father (Uther Pendragon) and the enemy (traditionally Mordred was Arthur's bastard child or nephew, possibly by his half-sister depending on the version). Han Solo isn't exactly the Lancelot type, but he does end up with the girl. Of course the Jedi are called knights! I don't see how anyone could come to the conclusion that Star Wars was not strongly influencec by Arthurian legends.