Costume: Middle East Militia Disguise
How to Unlock: Middle East - Militia Safe House. Go right at the third fork to find it in a locker.
Notes: Only useable in Act 1.

Costume: South American Rebel Disguise
How to Unlock: South America - Cove Valley Village. In one of the small houses, go inside to find it, use infrared to make it easier.
Notes: Only useable in Act 2.

Costume: Civilian Disguise
How to Unlock: Start Act 3.
Notes: Only useable in Act 3.

Costume: Suit
How to Unlock: Beat the game on any difficulty.

Costume: Altair
How to Unlock: Earn the Assassin's Emblem.
Notes: Makes Snake look like Altair from Assassin's Creed.

The FaceCamos allow you to change Snake's facial appearance. A couple are pretty nice, but a lot of them are just merely for fun and serve no real purpose at all. Note that you can only start unlocking FaceCamo on the Nomad by completing the Laughing Octopus fight in Act 2.

Camo: FaceCamo standard (needed to collect other FaceCamo)
How to Unlock: Defeat Laughing Octopus.
Effect: Increases chances of being spotted.

Camo: Young Snake
How to Unlock: Start Act 3.

Camo: Young Snake w/ Bandanna
How to Unlock: Start Act 3.

Camo: MGS1 Snake
How to Unlock: Start Act 4.

Camo: L. Beauty
How to Unlock: Defeat Laughing Beauty non-lethally.

Camo: R. Beauty
How to Unlock: Defeat Raging Beauty non-lethally.

Camo: C. Beauty
How to Unlock: Defeat Crying Beauty non-lethally.

Camo: S. Beauty
How to Unlock: Defeat Screaming Beauty non-lethally.

Camo: Otacon
How to Unlock: Bump into Otacon with the Mk. II during the Mission Briefing.

Camo: Raiden w/ Vizor
How to Unlock: Bump into Naomi with the Mk. II during the Act 4 Mission Briefing.

Camo: Raiden Vizor Down
How to Unlock: Bump into Sunny with the Mk. II during the Act 4 or any other Mission Briefing.

Camo: Roy Campbell
How to Unlock: Bump into Campbell with the Mk. II during the Act 1 Mission.
Briefing. To play this briefing, access Mission Briefings from the start menu.

Camo: Drebin
How to Unlock: Obtain at least 60 weapons.

Camo: Corpse
How to Unlock: Have 51 or more continues in a playthrough.
Notes: Able to convince soldiers you're dead by playing dead.

Camo: Big Boss
How to Unlock: Earn the Big Boss Emblem.
Notes: Same as Corpse FaceCamo, also scares enemy soldiers.