Here are some of the basic codes that I have found in various other sites:

God Mode=God
Fly=Fly
Ghost Mode=Ghost
(to disable Fly and Ghost Modes, type in walk as the cheat)
Level Select=SwitchCoopLevel[level name]
Spawn Item=Summon[item name]
Kill all other characters=KillPawns
First Person View=BehindView 0
Infinite Air=Amphibious

Cheats must be activated in order for codes to work.

Get Head= Summon Head Log in as admin(mp)= Adminlogin (adminpassword) Actiate cheats= CheatPlease