All Multiplayer Skins
Down, Left, Up, Left, Right, Down, Left, Up

Paintball Mode
Right, Left, Right, Left, Down, Down, Up, Up

Unlock all Artwork
Down, Right, Down, Right, Down, Up, Down, Down, Right, Down, Right, Down, Up, Down, Left

Unlock all levels in Campaign and multiplayer modes
Down, Right, Down, Right, Up, Down, Up, Left

Unlock all multiplayer skins, single and multiplayer levels and all content
Down, Right, Down, Right, Up, Down, Up

Unlock One Life Mode
Left, Down, Up, Right, Up, Right, Left, Down

Restore all Health and gain 100% Armor
R,R,R,L,R,R,L,R.

Restore eye power
L,R,L,L,L,R,R,L

All Eye Powers
L, L, R, R, R, R, L, L

Unlocks all maps
L, R, X, Y, X, Y, L, R, X, X, Y, Y, Z

Harpoon:
When you have a Harpoon and are trying to kill someone else with it, shoot the ground around their feet. This is much easier then trying to shoot the person's body. You may even kill more than one. Note: Do not try this with other weapons such as pistols, machine guns, commandos, etc.

Get Golden Gun
To find the golden gun you must be in the Hong Kong level after Dr. No's helicopter attacks the building(after you open the sliver case). Kill everyone on that level of the building but DON'T GO THROUGH THE HOLE TO PROCEED ONWARDS. Instead to back to where the sliver case was and look back the way you came. Go to your left and crouch down. You should be able to go through the wall(it's right next to some fire). Go straight through this hallway(still crouched) and you should be able to go through the wall to your left(next to the corner). Then you will be in a room with a cow in a boat. The golden gun is behind the cow.

Multi-player mode: Shields:
When your opponent uses his or her shield, hit them with your stun power. They will be unable to hack out of it because their shield drains all of their power. Then, pick them up and throw them. When your opponent uses MRI Vision, use your shield. You will become invisible to them. Try different combinations of weapons to see which works best for your fighting style.