I recently got my OXM from the mail, and they had a section where they interviewed Bungie about some of the stuff they had to cut out from the retail game. It's a pretty interesting read, though some we already knew. One of the main things they talked about was a level called "Guardian Forest" where the player went into a heavily forested area and met their newest enemy: The Guardians themselves. Whats cool about it, originally, If the player killed a Guardian, he/she was able to rip out it's laser eyeball and use it as a weapon! (I uploaded a picture of a Guardian from the magazine in the respective page - go check it out :P) Sadly though, Guardian Forest was completely cut - though the Multiplayer Map "Guardian" was the only thing to survive.
They also said they had to cut huge segments out of Tsavo Highway, which is a bummer since TH is one of my favorite levels in the game. Like I said, It's a pretty interesting read for all you guys out there; If you have the money, you should definitely check out OXM Issue #97 :)