doubleofive said:

I love how I remember somehow that it was changed because "A Jedi doesn't take revenge." Then I remember hearing that it was too similar to "Star Trek II: The Revenge of Khan", so they both changed their titles.

You're half right. The change from "Revenge" to "Return" had nothing to do with Star Trek II, which had been out for months when ROTJ's title was changed. Paramount changed the subtitle of Star Trek II from "The Vengeance of Khan" to "The Wrath of Khan" because at the time, ROTJ was still to be called "Revenge of the Jedi."

ST2 came out in June 1982, ROTJ in May 1983. Even though ST2's release date was a full year before ROTJ's, Star Wars was so big and anticipation for the third film was so high that Paramount worried that releasing a film with a title containing "Star ____" and "Vengeance of ____" would cause confusion and/or raise the ire of Lucas' legal department.

Irony: It was Paramount who came up with the "Vengeance of Khan" title in the first place. Obviously, someone else at the studio (maybe *their* lawyers?) then realized it wasn't a good idea. Memory Alpha says that Meyer himself brought up the ROTJ issue - he hated the studio's retitle and wanted them to go back to his original title of "The Undiscovered Country". I think William Shatner brought this up in his book "Star Trek Movie Memories".