According to the IMDb page for Star Wars Episode IV: A New Hope, James Earl Jones is uncredited for his voice of Darth Vader. Even though he is credited in the credits at the end of the film and it should be changed.
Chris: Apparently Jones wasn't originally credited in Star Wars (1977) or The Empire Strikes Back, at his own request. However, his name was added to the credits for the Special Editions. IMDb policy is to go by the original credits in determining whether someone was credited or uncredited.