There are three Avatar Awards you can unlock in Halo 4 for the Xbox 360, if you want to pimp out your Avatar in some Halo 4 gear.
I wish there were a few more, but this is what we get I suppose. I am kind of digging the Knight Helmet though.
Knight Helmet – Unlock the “Knight In White Assassination” achievement by assassinating a Knight in any Spartan Ops mission
Platinum Mark IV Helmet – Unlock the “Wake Up, John” achievement by completing the campaign on Normal difficulty or higher
UNSC Infinity Hoodie – Unlock the “Not Some Recruit Anymore” achievement by ranking your Spartan-IV up to SR-5