There are 45 different sets of Spartan armor in Halo 4 that can be unlocked by playing through Xbox 360's multiplayer.
Below is a list of all the unlockable armor, Examiner reported:
SPARTAN ARMOR
Rank Unlocks - Helmet/Torso/Left Shoulder/Right Shoulder
* Recruit - Default
* Warrior - SR-8
* Air Assault - SR-13
* Soldier - SR-15
* Aviator - SR-17
* Defender - SR-24
* Recon - SR-26
* E.V.A. - SR-27
* War Master - SR-37
* Scout - SR-38
* Orbital - SR-41
* Infiltrator - SR-42
* Hazop - SR-43
* EOD - SR-45
* Oceanic - SR-47
* Enforcer - SR-50
Commendation Unlocks - Helmet/Torso/Left Shoulder/Right Shoulder
* Mark VI: Complete the campaign on Legendary (Solo or Co-op)
* Commando - Dominion Victory Master
* Gungnir - Slayer Victory Master
* C.I.O. - Spartan Slayer Master
* Ranger - Combat Opportunity Master
* Venator - Assassin Master
* Protector - UNSC Loadout Master
* E.V.A. BRCH - Hail of Death Master
* Infiltrator TRAC - Multikill Master
* Defender CTRL - Bullet in the Brain Master
* Soldier ZNTH - Spartan Spree Master
* Recon Surge - Covenant Loadout Master
* Warrior Matrix - Forerunner Loadout Master
* Enforcer Tribal - Turret Mastery
* Protector Drift - Weapon Mastery
* Orbital AEON - Covenant Destroyer
* Aviator Bond - Wheelman Mastery
* Air Assault Verg - Vehicle Mastery
* Venator Raptor - Backstab Mastery
* Soldier Zenith - Spartan Spree Mastery
* Ranger STRK - Protector Mastery
* EOD Shadow - Hail to the king Mastery
* Vanguard Converge - Flag Victory Mastery
* Scout APEX - Oddball Victory Mastery
* Commando FRCT - Flood Victory Mastery
* Contoured arms CHVR - Perfection Mastery
* Recruit Legs Tiger - Exterminator Mastery
* Twin-Plated AEON - Close Quarters Mastery
* Contoured leg CHVR - Payback Mastery
Forearms
* Recruit - Default
* Twin-plated - SR-9
* GV-09 Locking - SR-22
* Inner-plated - SR-30
* Outer-plated - SR-34
Legs
* Recruit - Default
* RG-63 Counter - SR-10
* LG-50 Bulk - SR-23
* Outer-plated - SR-31
* XG-89 Narrow - SR-35
* Recruit TIGR - Exterminator - Master Commendation
* Contoured SHRD - Payback - Master Commendation
Visor
* Recruit - Default
* Frost - SR-29
* Solar - SR-20
* Frost - SR-29
* Midnight - SR-46
* Sunspot - Assistant - Master Commendation
* Blindside - Avenger - Master Commendation
* Cyan - Brink - Master Commendation
* Verdant - Splatter - Master Commendation
* Legendary - Complete the campaign on Legendary (Solo or Co-op)
Spartan Points (SP) and Service Points (SR) can be earned as you gain experience in Halo 4's War Games multiplayer, Spartan Ops co-op or Forge world building. As Players progress upward through Service Ranks and as they earn commendations, they can unlock Spartan Armor customizations.