When the ship Anakin and Obi-Wan are on at the start begins firing on an enemy ship, there is some footage of explosions and guys being thrown into the air. One of them screams a classic "Wilhelm" scream.
We see in the movie that General Grievous is permanently coughing when he talks. The cause of this can be found in the last episode of the animated, Emmy-winning TV series "Clone Wars." In that episode, Grievous kidnaps Palpatine and before leaving into space, he is attacked by Mace Windu, who destroys part of his armor in the chest, making him cough for the first time.
George Lucas makes a cameo appearance during the opera scene. He is the blue faced being, named Baron Papanoida, that you see outside Palpatine's box. It marks Lucas' first and only appearance in any of the Star Wars films; also in that scene is Lucas' daughter Amanda and her boyfriend. Lucas also reportedly provides the sound of General Grievous' coughing.
Hayden Christensen wanted to wear the Darth Vader suit in the films, as it had always been a dream of his (revealed in the DVD commentary). Though the filmmakers hesitated, as Christensen was too short, they eventually let him wear the suit onscreen, but Christensen had to look through the mouth-piece of the Darth Vader costume, not the eyes.
As Obi-wan and Anakin deliver Palpatine to the Jedi Council on Coruscant, look carefully at the lower right-hand part of the screen and you'll see the Millennium Falcon landing as well (confirmed by George Lucas).
Anthony Daniels (C3PO) has the last line in this film and the first line in A New Hope.
George Lucas purposely made the Darth Vader suit uncomfortable, heavy, and cumbersome. This way, as Hayden Christensen walks around in the armor (especially after first being put into it), his movements seem awkward - after all, Darth Vader isn't used to wearing it yet.
Gary Oldman was originally supposed to provide the voice of General Grievous, but he backed out after learning the film was to be made outside of the Screen Actor's Guild, of which he is a member.
The blue-skinned Twi'lek Jedi Aayla Secura, who can be seen in this film and "Attack of the Clones", was not created by George Lucas. She originated in the Star Wars comic books from Dark Horse. After seeing a cover painting, George Lucas became so impressed that he decided to use her in the movies.
Exactly six years apart, this film was released on the same day as Episode I. "Star Wars" and "Return of the Jedi" were also released on the same day, six years apart.
George Lucas' three children play cameos. Jet is a young Jedi called Zett Jukassa. Amanda plays a character called Terr Taneel, and Katie plays a blue-skinned alien called Chi Eekway, both visible when Palpatine arrives at the senate after being saved by the Jedi.
Rick McCallum's daughter, Mousy, appears as one of the Padawans killed by Darth Vader in the Jedi Temple.
In the first shot of the space battle at the beginning, just before the camera pans down to Obi-Wan and Anakin's fighters, a piece of debris hits a spaceship. Closer inspection reveals that this is a kitchen sink.
This is the first Star Wars movie to recieve a rating higher than "PG."