From the main menu of disc two, select the "Humans Only" door. Once in, click on "Production Tour". Once the tour starts playing, use your chapter skip to get to the end of the tour (or, if you're so inclined, feel free to watch the tour). After the tour, a menu screen will appear filled with doors (and which will look somewhat similar to the opening credit sequence). Seven of these doors are selectable; each one will bring you to an Easter egg. Here are the contents of each door, listed left to right by row:
Door 1 will lead you to a short video piece in which John Lasseter and Darla Anderson talk about the huge atrium in Pixar's new building. Following this, you'll be led to a sketch gallery of Pixar staffers' humorous ideas on how to use the atrium (parking lot, artillary stagings, hedge maze, and so forth).
Door 2 will lead you to a short clip of a monkey "animating" a scene from the movie.
Door 3 will lead you to an early animation test for the film: a tie conversation between Johnson (an early version of Sulley) and an armless Mike. (This test is also found in the "Animation" section under "Early Tests", but that version covers the test's dialogue with audio commentary. The Easter egg version presents the test with its original dialogue.)
Door 1 will lead you to a brief clip from the movie of Sulley scaring a child.
Door 2 will lead you to an outtake from the DVD introductions shoot, in which an overtly active monkey cracks up the Pixar staff.
Door 3 will lead you to the DVD credits.
Door 4 will lead you to another monkey-related blooper from the DVD introductions shoot.
Reviews: DVD Talk also has a review of
Monsters, Inc. by Aaron Beierle.