Press '~' during game-play to bring up the console then type 'BeMyMonkey'to enable cheat mode and then enter the following codes. To disable the cheats enter 'BeMyMonkey' again.

Bemymonkey: Toggle Cheat Mode

God: Toggle God Mode
loaded: All weapons
Allammo: Gives 999 ammo
SetWeaponFire (0 or 1): Weapon Firing
fly: Flight Mode
walk: Normal movement (deactivates noclip or fly mode)
Open (map name): Map Select
nextlevel: Warp to next map level
Invisible [1 or 0]: Turn on (1) or turn off (0) invisibility

SetWeaponTrick [1 or 0]: Turn weapon trick on or off

Amphibious: Underwater Mode
behindview: 1 for 3rd person view, 0 for normal 1st person

freecamera: 1 to enable free camera movement, 0 to disable

ghost: Activate Noclip mode

toggleservos: Animation Servos

difficulty(number): Change Game Difficulty

ManCannon(number): Damage All Visible Pawns

ToggleSpeed: Double Speed

togglehud: Enable/disable Heads-Up Display

phoenix: Enable/disable Phoenix Powersuit

EnableFreeOrders: (0 or 1) Free Orders

ToggleFreezeView: Freeze View

GibHitNPC: Gib NPC Under Crosshair

GodEx (actor): God Mode For Selected Actor

HurtMe (number): Harm Player A Specific Amount

ToggleImpacts: Impacts

Actors: List All Actors

PO: Players Only

ToggleRMode: Rmode

ToggleScoreBoard: Scoreboard

CheatView (actor): See View From Indicated Actor

SetCameraDist (number): Set Camera Distance

SetJumpZ (number): Set Jump Height

SetParticleDestiny (number): Set Particle Destiny

SetEyeHeight: Set Player Eye Height

SetMyHealth (number): Set Player Health
ChangeSize (number): Set Player Size

SetSpeed (number): Set Player Speed

ShowTeams: Show Player Teams

SloMo (number): Slow Motion

Sum (item name): Spawn Indicated Item

DamageNPCs (number): Specify Damage to NPCs

Damage (number, target): Specify Damage to Target

SetHealth (number, Target): Specify Health to Target

Goodies (number, number): Summon Array of Goodies

ViewSelf: Target Camera on Player

teleport: Teleport to location at crosshairs

ToggleShowAll: Show Hidden Actors

ToggleShowKPs: Show Keypoints

ToggleShowNPs: Show Navigation Points
ToggleTimeDemo: Time Demo

Toggleinfiniteammo: Toggle Infinite Ammo

ToggleInvisibility: Toggle Invisiblity

ToggleReloads: Toggle Reloads

KillHitActor: Kill Actor Under Crosshair

killactivenpcs: Kill all active NPC entities