Full H4 Armor Unlocks

Sourced largely from Halo4Nation.com:

Complete list of helmet and visor unlocks with rank or accomplishment requirements listed.  The "Level" column either represents the rank you need to reach, or the number of items you need to accomplish. For example, "Spartan Slayer Mastery" requires that you kill a total of 4,725 players in War Games matchmaking.  The "Difficulty" column represents my grading of relatively difficult each item is to get.

Type	Requirement	Level	Difficulty
Recruit Helmet	Starting Armor	-	0
Recruit Visor	Starting	-	0
Fotus Helmet	Limited Edition Halo Xbox	-	1
Strider Helmet	War Games Map Pass or Limited Edition Halo 4	-	1
Deadeye Helmet	Pre-order from BestBuy / Play.com	-	1
Locus Helmet	Pre-order from Future Shop or King of the Hill app	-	1
Scanner Helmet	War Games Map Pass or Limited Edition Halo 4	-	1
Hazop Helmet	Rank Based	SR-43	2
Infiltrator Helmet	Rank Based	SR-42	2
Oceanic Helmet	Rank Based	SR-47	2
Orbital Helmet	Rank Based	SR-41	2
Recon Helmet	Rank Based	SR-26	2
Scout Helmet	Rank Based	SR-38	2
Soldier Helmet	Rank Based	SR-15	2
E.O.D. Helmet	Rank Based	SR-45	2
Aviator Helmet	Rank Based	SR-17	2
Defender Helmet	Rank Based	SR-21	2
War Master Helmet	Rank Based	SR-37	2
E.V.A. Helmet	Rank Based	SR-27	2
Air Assault Helmet	Rank Based	SR-11	2
Solar Visor	Rank Based	SR-20	2
Frost Visor	Rank Based	SR-29	2
Midnight Visor	Rank Based	SR-46	2
Enforcer Helmet	Rank Based	SR-50	3
Warrior Helmet	Rank Based	SR-8	4
Wetworks Helmet	Rank Based	WK-4	4
Pioneer Helmet	Rank Based	PR-4	4
Engineer Helmet	Rank Based	EN-4	4
Tracker Helmet	Rank Based	TK-4	4
Rogue Helmet	Rank Based	RG-4	4
Stalker Helmet	Rank Based	SK-4	4
Pathfinder Helmet	Rank Based	PT-4	4
Operator Helmet	Rank Based	OP-4	4
Wetworks Visor	Rank Based	WK-6	4
Pioneer Visor	Rank Based	PR-6	4
Engineer Visor	Rank Based	EN-6	4
Tracker Visor	Rank Based	TK-6	4
Rogue Visor	Rank Based	RG-6	4
Stalker Visor	Rank Based	SK-6	4
Pathfinder Visor	Rank Based	PT-6	4
Operator Visor	Rank Based	OP-6	4
Raider Helmet	Halo Waypoint Classified Unlock	-	5
Mk. VI Helmet	Complete the campaign on Legendary	-	6
Legendary Visor	Complete the campaign on Legendary	-	6
C.I.O. Helmet	Spartan Slayer Master	4725	7
Ranger Helmet	Combat Opportunity Master	885	7
Sunspot Visor	Assistant Master	1825	7
Gungnir Helmet	Slayer Victory Master	535	8
Venator Helmet	Assassin Master	140	8
Blindside Visor	Avenger Master	675	8
Verdant Visor	Splatter Master	165	8
Cyan Visor	From the Brink Master	375	9
Vanguard Helmet	Forerunner Enemy Mastery	12965	10
Commando Helmet	Dominion Victory Master	240	10
Protector Helmet	UNSC Loadout Master	8105	10