There are two versions of the game:
Regular: Comes with the ODST Campaign, Firefight, and Theater on one disk, and Halo 3s Multiplayer, Custom Games, Forge, and Theater on the other.
Special Edition: Same as regular except for a limited edition Superintendent wireless controller.
For information on the Johnson pre order bonus go here.
Edit: Also all versions of the game will grant you the ability to access the Halo Reach beta. When the beta is released (unconfirmed release date) you can get it through the "Extras" tab from the main menu.
~Hunter
[Edited on 06.25.2009 11:29 AM PDT]