During play, press ~ to open the console. Enter BeMyMonkey to enable cheats. Now enter any of the following at the console:

God                               God Mode 
Invisible                         Invisibility 
Loaded                          All weapons 
AllAmmo                        Full ammo
GodEx(actor)                  God Mode for the given actor 
Phoenix                         Phoenix Powersuit 
FearMe                          Enemy now fears you 
Ghost                             Ghost mode 
Fly                                 Fly mode 
Amphibious                   Underwater mode 
Walk                             Normal walking mode 
SloMo(#)                       Slow motion   
SetJumpZ(#)                 Set jump height 
ToggleInfiniteAmmo    Toggle Infinite Ammo 
ToggleReloads             Toggle Reloads 
ToggleInvisibility         Toggle Invisibility 
Teleport                       Teleport to spot the player is looking at 
NextLevel                    Skip to next level 
Open(mapname)          Open Map x 
ToggleSpeed               Double speed 
SetSpeed(#)                 Set player speed 
ChangeSize(#)             Set player size 
Goodies(#,#)                 Summon an array of goodies (see below) 
Sum(Item name)          Summon item (see below)
Actors                          Full actor list 
GotoActor(Name)         Change location to the given Actor 
Damage(#,Target)        Damage target by the specified amount 
DamageNPCs(#)           Damage NPCs by the specified amount 
SetHealth(#,Target)      Set health to the specified amount for target 
SetMyHealth(#)             Set player health to the specified amount 
HurtMe(#)                      Hurt the player by the specified amount    
ManCannon(#)              Damage all visible pawns 
ToggleServos               Toggle animation servos    
ShowTeams                 Show player teams 
Difficulty(#)                   Change game difficulty 
CheatView(x)               See view from specific actor
ViewSelf                       Target camera on player 
ToggleTimeDemo            Enable time demo 
ToggleScoreBoard           Toggle scoreboard 
EnableFreeOrders(0/1)     Toggle free orders 
BehindView                   Toggle Behind View 
SetParticleDensity(#)     Set particle density    
ToggleImpacts              Toggle impacts 
SetWeaponTick(0/1)       Toggle weapon tick code 
SetWeaponFire(0/1)      Toggle weapon firing 
ToggleShowAll            Show all hidden actors 
ToggleShowKPs          Show all keypoints 
ToggleShowNPs          Show all nagivation points 
ToggleRMode               Toggle RMode    
SetEyeHeight                 Set player eye height 
KillActor(x)                     Kill specified actor 
KillHitActor                     Kill actor under crosshair 
KillHitNPC                      Kill NPC under crosshair 
KillActiveNPCS              Kill all active NPCS 
KillDormantNPCS          Kill all dormant NPCS 
GibAllNPCS                   Gib all NPCs    
GibHitNPC                     Gib the NPC under the crosshair 
PO                                 Toggle players only 
ToggleFreezeView      Toggle Freeze View 
ToggleHUD                   Toggle HUD 
SetCameraDist(#)         Set camera distance    
FreeCamera(0/1)          Toggle free camera movement 

Item names:
Use these with the 'Sum' code above.
 

ammoAssaultRifle
ammoEnergyRifle
ammoFlameThrower
ammoGrenadeConcussion
ammoGrenadeEMP
ammoGrenadeFragment
ammoGrenadeIncendiary
ammoGrenadeToxic
ammoLaserRifle
ammoPistol
ammoRocketLauncher
ammoShotgun
ammoSmokeGrenade
AutoTurretPickup
FieldGeneratorPickup
ProximitySensorPickup
RocketTurretPickup
weaponAssaultRifle
weaponEnergyRifle
weaponFlameThrower
weaponGrenadeLauncher
weaponLaserRifle
weaponLeechGun
weaponPistol
weaponRocketLauncher
weaponShotgun
weaponSingularityCannon
weaponSniperRifle
weaponTakkra