Press [Ctrl] + [Alt] + [Shift] + D during game play and
watch your money increase. Repeat to get more money. 

Note: Do not do this too many times or you will end up 
with a negative amount.

Also, this changes the "Help" button to "Debug". In debug
mode, there are some interesting things. You can go up or
down a grade (all the way up to five star).