I just found this on the Science Fiction News of the Week site:
Lucas Teases Episode III Title
Star Wars: Episode III director George Lucas told USA Today that fans have already guessed the upcoming prequel's titleóbut added that he won't announce it until November, when the first trailer hits theaters. The guesses include Rise of the Empire, but Lucas told the newspaper: "No, that's not it."
Is it Revenge of the Sith? Lucas smiled knowingly, backed away and teased the newspaper: "That's a possibility. Lots of titles out there." Episode III opens in May 2005.