During play, press Enter and type the following cheat codes : 

-embiggenme      God mode 
-crazyguy        All spells
-whoah           Fly mode
-uberload        Random level skip 
-showfps         Show frame rate
-calcfps         Calculate frame rate
-debug           Debug info
-boundingbox     Draw bounding box around object
-3dnow!          AMD support on/off
-cswire          Landscape on/off