Various Cheats:
Open console with the ~ key then type one of the following

REB GOD - God Mode

REB INFINITE AMMO - Unlimited Ammo

NEXT LEVEL - Skip current level

GIVE [ITEM] - Get Item

GIVE AND EQUIP [ITEM] - Give & Equip (See list below)

Items:
LASER
BINARY_LASER
MAXIM_LASER

BATTERY_PLUS
PLASMA_PISTOL
PLASMATRIX
PLASMAGNUM

AUTOLOCK_BOLTS

GRENADE_LAUNCHER

GRENADE_PLUS
GRENADE_EMP

MISSILE LAUNCHER
MISSILE_PLUS
MISSILE_EMP
FLAMETHROWER
NANOFRAG
EPULSAR

Keys:
KEY
KEYB

Shield:
SHIELD_PICKUP = Standard Shield
ARMOUOR_PICKUP = Heavy Shield

Body Slot Upgrade Pickup:
AIM_ACCURACY_PICKUP
LOCK_DECODER
BEACON_TRACKER
TERRAIN_SCANNER
TERRAIN_SCANNER_WITH_RADAR
OMNI_SCANNER
HOLOGRAM_GENERATOR
AUDIO_CLOAK
SIGHT_PICKUP
SIGHTPLUS_PICKUP