Remember Gandalf hitting his head during his first scene in Bag End? Apparently it was an accident but Ian McKellen did such a great job acting through it that Jackson kept the take. (Source)

Sir Christopher Lee was the only cast member to have met Tolkien. Tolkien gave him permission to play Gandalf but Lee ended up as Saruman.(Source)

Eight out of the nine fellowship actors got a tattoo that says "nine" in Tengwar. John Rhys-Davies sent his stunt double to take his place.(Source)

Peter Jackson has a quick cameo in Bree (he's the dude holding the carrot).(Source)