Dawson Casting: In the Prologue, Sir Ian Holm is very briefly seen wearing a dark, curly wig, as Bilbo 50 years younger. While Gandalf does say that Bilbo "hasn't aged a day" since seeing him last, Holm is obviously too old to have such brown hair.
Enforced Method Acting: When the dragon firework goes off at the party, the shriek heard is Billy Boyd actually screaming, as he was unaware at the time that the firework was really going to explode on-set (he thought that it would be in a separate shot). It was not scripted, but the take ended up in the final cut.
While filming the final fight scene, Viggo Mortensen was nearly killed when a stuntman accidentally threw a real knife (the stunt called for a rubber fake, for obvious reasons) straight at his head; due to the swordsman skills he learned (and/or sheer luck), he managed to deflect it.
During filming for Sam's big emotional moment at the end, Sean Astin stepped on a large shard of glass that went right through his foot. Luckily they managed to get him airlifted to get it removed and fixed.
When Gandalf visits Bilbo at Bag End, Ian McKellen bumps into the low hanging lanterns, which was expected. Then he turns quickly, and whacks his head on a wooden beam in the low ceiling, which was not expected. Since it looked just fine and also pretty funny, it was kept as the final cut.
Aragorn and Lurtz's fight is a lot more real than intended. Lurtz's actor threw the wrong knife instead of the safe prop, which made it quite lucky that Viggo Mortensen successfully deflected it. Lurtz's actor also could not see well in the costume, so many of his blows actually connected, which prompted Mortensen to go stiff on his own blows.
Troubled Production: An entire action sequence ended up getting scrapped due to torrential rains causing a massive flood that washed away the set where it would have been filmed.
Written-In Infirmity: Christopher Lee broke his left hand after he slammed it on his hotel door. The injury is obviously seen as Saruman jeers at the Fellowship's plight on Caradhras.
2002 Video Game
Promoted Fanboy: While the PC and PlayStation 2 versions use Scott Menville, The Xbox version of the game instead features Cliff Broadway, known in the Tolkien fandom as TheOneRing.net staff member Quickbeam, as the voice of Samwise Gamgee.
Stillborn Franchise: A sequel, titled The Treason of Isengard, was announced but cancelled when the project was not meeting Vivendi Universal's expectations.