You will receive the following (if it's not listed directly below, it's not included):

2 x Discs
Game Case
Graphics/Artwork insert

OVERVIEW:

Complete 2 disc set with storyboards. This is not the Halo game or an expansion pak and will not work without the Halo 3 game disc.

Disc One

Only compatible with the Xbox 360.
Included in both Collector's and Legendary editions.
A/V calibration tool.
Exclusive Halo 3 gamer pictures and dashboard theme.
Gallery of concept and production art (set to music).
The popular internet flash game Warthog Launch.
Bungie guided network set-up.
Typical day at Bungie Studios.
Making of Halo 3.

Disc Two

Usable on anything that plays standard DVDs.
Only included in the Halo 3 Legendary Edition.
Completely remastered, high resolution versions of the Halo and Halo 2 cinematics with 5.1 audio and an optional "Director's Commentary" track featuring Martin O'Donnell, Joseph Staten, and Jason Jones.
Bestiarum: An expanded digital guide to the creatures, cultures, and worlds of Halo 3, with art and assets exclusive to this interactive edition.
The Cortana Chronicles:Jen Taylor, the voice of Cortana, takes us on a tour of the worldwide Halo fan community, where she meets Halo fanatics from near and far, obscure and famous alike.
All-new, exclusive Machinima episodes from Red vs Blue and This Spartan Life, as well as a novel "mockumentary" voiced by Sgt. Johnson himself, David Scully.