Below is a list of all available armor in Halo 4 and a the requirements to unlock them,

 
SPARTAN ARMOR SETS

Unlocked at the required SP rank – 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

Unlocked by completing the required commendation – 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 Colour

Recruit (Blue) – Default
Solar (Red) – SR-20
Frost (White) – SR-29
Midnight (Black) – SR-46
Sunspot (Purple & Blue) – Assistant – Master Commendation
Blindside (Dark Red)– Avenger – Master Commendation
Cyan (Light Blue) – Brink – Master Commendation
Verdant (Green) – Splatter – Master Commendation
Legendary (Gold) – Complete the campaign on Legendary (Solo or Co-op)