"Press ~ before you type these:
god                 - Enables god mode
g_unlimited_ammo 1  - All ammo gets stuck at 999
noclip              - Turn off clipping
notarget            - Invisibility
map end             - Jump to the level end boss 

Also, you can type 'give <name of weapon/ammo> and # of ammo'
ex: for 100 shotguns, type 'give shotgun 100'"
