Two more images for the edition exclusives, both images borrowed directly from the Bungie Weekly Update:
http://www.bungie.net/News/content.aspx?type=topnews&link=BWU_042310So the four I have seen so far are:
Limited Edition => Elite Armor
Legendary Edition => Flaming Helmet Armor Effect
Pre-Order Exclusive (confirmed at Game Stop, Amazon, Best Buy, probably many others) => Recon Helmet Variant
Game Stop Pre-Order Exclusive => "UA Multi-Threat Mjolnir Mark VI(B) Armor" (aka the "Beer Can Belt") BCB, anyone?
The product description for the Legendary Edition states that it includes everything from the Limited Edition, so we are left to assume that the Legendary Edition gets you both the code for the Elite Armor set and the code for the Flaming Helmet Effect.
Pre-ordering from Game Stop is supposed to get you both the generic pre-order exclusive code for the Recon Helmet was well as the Game Stop-specific pre-order exclusive code for the BCB.
Halo Reach Limited Edition Xbox comes with the Standard Edition of Reach, so it's "No Codes For You!" if you go that route only... but man what a nice looking console!