One of the cool little add ons in Halo 3 is that you get the ability to customize your multiplayer avatar.  In the Halo 2 you could choose to be a Spartan or an Elite and then change your armor's color.  Well in Halo 3 you can go beyond that and you have the ability to actually change your armor.

You start out with the basic armor Master Chief wears in the game but as you complete special tasks you unlock new armor.  These special tasks unlock shoulder guards, chest plates and helmets.  The link below is to a site that allows you to check out the different types of armor and allows you to find your ideal look and then tells you how to unlock that armor.  Also if you see someone online with a flaming helmet, they work for Bungie so try not to smack talk to them or you might get banned.

http://php.badrouter.net/bnet/