All these codes have to typed in the TALK console (default key [T])

 god   - God mode
 ammo   - Gives full ammo
 guns   - Gives all guns
 health  - Gives full health
 armor   - Gives full armor
 poltergeist  - Invisibility On/Off
 pos   - Show position On/Off
 baddaboom  - Huge explosions
 maphole  - Complete mission
 build          - Show version On/Off
 mods           - Get all modifications for all weapons

 skillz         - Hmm, left over from NOLF 2?