Weapons and items:

Press ~ to display the console, then type "give(place item name here)" using the following 
information. Other choices include "give all", "give weapons", or "give ammo". 

Item Names
ChainFist
ETF Rifle
Plasma Beam
Prox Launcher
Tesla
Double Damage
Hunter Sphere
Defender Sphere
Vengeance Sphere
A-M Bomb
IR Goggles
Doppleganger
Flechettes (ETF Rifle ammunition)
Prox (Prox Launcher ammunition) 


Level select:

Press ~ to display the console, then type map "name" using the 
following information.

Level code                     Name      
Single player

RMINE1                      Lower Mines                   
RMINE2                      Mine Engineering              
RLAVA1                      Thaelite Mines                
RLAVA2                      Tectonic Stabilizer           
RWARE1                      Eastern Warehouse             
RWARE2                      Waterfront Storage           
RBASE1                      Logistics Complex           
RBASE2                      Tactical Command              
RHANGAR1                    Research Hangar               
RHANGAR2                    Maintenance Hangars           
RSEWER1                     Waste Processing              
RSEWER2                     Waste Disposal                
RAMMO1                      Munitions Plant               
RAMMO2                      Ammo Depot                   
RBOSS                       Widow's Lair                  
   
Multi-player

RDM1                        The Low Road                 
RDM2                        The High Road                 
RDM3                        Boxed In                     
RDM4                        Razor Close                  
RDM5                        Stone Hinge                  
RDM6                        Nexus                        
RDM7                        Sewer Citadel                 
RDM8                        Styx and Stones             
RDM9                        Scenic Overlook               
RDM10                       Great Divide                  

RDM11                       Dish It Out                  
RDM12                       Fall From Grace               
RDM13                       Roads To Nowhere              
RDM14                       Rogue's Edge                  
   
Other maps

RUNIT2                      Weapon and ammo depot         
RUNIT3                      Weapon and ammo depot         
RUNIT4                      Weapon and ammo depot         
 

Thanks to Revolution reader Freeloader!