Soon your time spent with Halo: Combat Evolved PC as far back as 2003 will be worth a bonus visual unlock in In September 2010's Halo: Reach. How's that for rewarding dedication?
Bungie staffer Roger "Sawnose" Wolfson recently re-confirmed on the Bungie message boards that owners of Halo: CE PC, who have authenticated their keys on Bungie's servers, will be able to use those keys to unlock a bit of "visual flair" for Halo: Reach. This unlock will not be from the game's Armory, though--it'll just be a little visual nod to some of the most hardcore Halo fans.
To get the bonus, you'll need to have your original CD key for Halo: CE PC on-hand. Said key will also need to have been authenticated--assuming you entered an online lobby at some point during your ownership of the game--before May 26, 2010.
Why then? Because Bungie has pulled data from that date and will be validating unlocks against it in a move to keep seedy people from using programs to generate a key. I should note that even if you bother with purchasing a new copy for this treat, Bungie will assume the fresh key has been key-genned.
No other details are being provided at this time, however, "Sawnose" says solid information, which will include how to use the key in-game, should be coming in the next few weeks as Reach's release date creeps ever closer.
Big ups to RageGummy for dropping the initial intel in our forums.