Director Peter Jackson Makes a Cameo
Peter Jackson, the films director, makes a cameo appearance in the movie, just as the Hobbits enter the town of Bree. Jackson is one of the guys that walks by before they enter into the Prancing Pony.
Watch carefully when Gandalf is inside Bilbo Baggins house. Take note when Gandalf talks to Bilbo in front of the mantlepiece. Above there are photos of Bilbo's parents. The people in the Photos are Peter Jackson and his wife.
Stone Trolls From "The Hobbit"
Just after the scene where Frodo is stabbed, he is taken into the woods. If you look at the background where Strider put down Frodo, you can see the 3 trolls that turned to stone from the book, The Hobbit.