At MJ's Face-R-Us Plastic Surgery you can enter coupon codes to unlock additional face and body skins of the developer's friends, fellow indie developers, etc.

Contact me if you find more.

MJ's Face-R-US Plastic Surgery can be found in the Northwestern quadrant of the map, near the Robson Zone and next to a Spray 4 Pay. It's location can also be found in the in-game map.

These are all the coupon codes found so far:

CARBONI
Anthony Carboni, the host of SGNL, Random Encounter and Casual Friday.

DTOID
Members of the Destructoid staff.

ELECPLAY
Members of the Electric Playground staff.

EMT
Members of the Epic Meal Time cast.

GAIJIN
Gaijin Entertainment, the developers of Bit.Trip.

MAXIMEAMIS
The friends of one of the game's artists.

MOJANG
Mojang AB, the developers of Minecraft.

ROMERO
John Romero, the creator of Doom.

PJFP
PJ "Fresh" Phil Guerrero from YTV.

POLYTRON
Polytron Corporation, the developers of Fez.

POWER
Dan Adelman of Nintendo of America and Chris Hoffman, former editor of Nintendo Power.

TEAMMEAT
Team Meat, the developers of Super Meat Boy.

URNOTE
Members of the Sony Entertainment staff.