During play, press TAB to bring down the console, then enter the following cheats:

god               God mode
dopefish          God mode, All weapons, 10 grand
allammo           Full ammo
fly               Flight mode
ghost             No clipping
walk              Disable fly and ghost
behindview 1      Third person view
behindview 0      First person view
sptravel(name)    Level select
   
Use the following level names:

SP0M0-TheLab.dvs
SP0M0-TheLab2.dvs
SP0M1-SomaSunset.dvs
SP0M2-Chinatown.dvs
SP0M3-TopOTheTower.dvs
SP0M4-TheRock.dvs
SP0M5-Embarcadero.dvs
SP1M1-UrbiaSouth.dvs
SP1M2-UrbiaAsylum.dvs
SP1M3-UrbiaNorth.dvs
SP1M4-Docks.dvs
SP2M0.dvs
SP2M1-MarketMadness.dvs
SP2M2-CardboardCounty.dvs
SP2M3-TheAquifers.dvs
SP2M4-IchthyaSouth.dvs
SP2M5-IchthyaNorth.dvs
SP3M1-Chozo.dvs
SP3M2-RiversOfWaste.dvs
SP3M3-Zangai.dvs
SP3M4-Transit.dvs
SP3M5-Bukko.dvs
SP3M6-BukkoRoof.dvs 

   

Thanks to Revolution readers THEchamberPOT_?, The_old_eYe and Barrney!