Enter these during gameplay without pausing:

Code Effect

L, L, R, B, B, A, A, R Armor
Up,Down,Left,Right,X,Y,L,R cloud
L, R, X, Y, A, B, Up, Down Explosive Pistol Round
L,L,R,A,A,B,B,R health
Up,Down,Left,Right,B,Y,R,L Hurricane
Up,Down,Left,Right,A,X,R,L lots of rain
Up,Down,Left,Right,Y,A,L,R rain
Up,Down,Left,Right,A,B,L,R sunny
R,X,X,Y,Y,R,L,L wanted level down
L,L,R,Y,Y,X,X,R wanted level up
R,Up,B,Down,Left,R,B,Right weapons 1 (grenade, nightstick, pistol, minigun, assault, micro smg, stubby shotgun)
R,Up,A,Down,Left,R,A,Right weapons 2 (molotov, teaser, dual pistols, flamethrower, carbine, smg, dual-barrel)
R,Up,Y,Down,Left,R,Y,Right weapons 3 (mine, chainsaw, revolver, flamethrower, carbine, smg, dual-barrel)
R,Up,X,Down,Left,R,X,Right weapons 4 (flashbang, bat, pistol, rpg, carbine, micro smg, stubby shotgun)

Unlockables

Bulletproof Taxi's - Complete dropping off 15 people in a row without the timer running out and all taxi's will become bulletproof while you are in them. This will not affect number of times cheated in the stats menu.

Trophies - Achieving certain tasks will reward you trophies, which can be found on the Trophy Shelf in your apartment.

Unlockables

Diamond Pillbox Unlock By Selling hallucinogens
Golden Binoculars Discovering 40 drug dealers
Jeweled Bong Unlock By Selling Depressants
Jeweled Key to the City Own all 21 safe houses in the city
Platinum Syringe Purchase Heroin
Silver Safe Make a $2000 profit
Titanium Briefcase Find all 80 dealers.
Wooden Spoon Achieve a loss of $500

Unlockables

Discount on the Ammu-nation store Score gold medals on all weapons at the Gun-Club
Gold medal Attain a score of 10000 or more for a weapon.
Immunity to Fire Get a Gold in the Fire truck Minigame
Increased body armor strength Complete all 5 waves of vigilante missions with 100% kill rate
Infinite Sprint Complete 5 Paramedic Missions
Regenerating health Beat both noodle delivery missions (to gold ranking)
Upgraded delivery bag Beat both mail courier missions (to gold ranking)