Start the game with the "-console" command line parameter and then press ~ in single player mode. Now you can enter one of the following codes:
Enable God mode: god 1
Disable God mode: god 0
Infinite ammunition: freeammo
Add experience to selected character: xp [number]
Add money to entire party: cash [number]
Gains 2 ranks in all disciplines: addalldisciplines
Spawn specified item: addthing [item name]
Remove money from entire party: dropcash [number]
Disable enemy and party AI: ai
Display frame rate: framerate 1
Location stats: whereis
Poison yourself: poisonme
Stake yourself: stakme
Disease yourself: diseaseme
Damage yourself: damage me
Frenzy yourself: frenzyme
Pause game: pause
Resume game: resume
View ending credits: endgame