During play, type in the following codes and press Enter to activate:

boxesCollision boxes around objects    
clearcClear caches      
diagsDisplay diagnostic   
dload Return to windows 
flyFlight mode       
getalifeUnlimited lives   
gotoLevel skip        
normalNormal game speed 
pedeCreate centipede   

reportGenerate reportfiles
robotAuto firing & movement until player takes control     
showzScreen modes      
slowSlower game speed  
slowwEven slower game speed 
slowwwEven slower than above       
slowwwwIncredibly slow    
timesTime codes        
wimpGod mode          

Thanks to Revolution reader Mike Scott!