Press [~] in the game and type in:

 god             God mode
 allammo         999 shots for all guns
 fly             Fly mode
 ghost           Ghost mode, walk through walls
 walk            Turns off "fly" and "ghost"
 behindview 1    3rd Person View
 open [mapname]  Starts a special level, where [mapname] may be:

                 AR-Asteroid
                 AR-Barracuda
                 AR-Luna
                 AR-Orbital
                 AR-Sequoia
                 AR-Sky
                 AR-Tut
                 Autoplay
                 Entry
                 Nerf
                 Nerf-Plaza
                 PM-Amateur
                 PM-Asteroid
                 PM-Barracuda
                 PM-Champion
                 PM-Luna
                 PM-Orbital
                 PM-Sequoia
                 PM-Sky
                 PM-Tut
                 PMX2-Luna
                 PMX-Asteroid
                 PMX-Luna
                 PMX-Orbital
                 RR-Amateur
                 RR-Asteroid
                 RR-Barracuda
                 RR-Champion
                 RR-Luna
                 RR-Orbital
                 RR-Sequoia
                 RR-Sky
                 SH-Asteroid
                 SH-Barracuda
                 SH-Luna
                 SH-Orbital
                 SH-Sequoia
                 SH-Sky
                 SH-Tut