Growing cities:
While playing a game, press [Tab]. Then, type "viagra" at the green cursor at the bottom of the screen.

Codes:

     CTRL-M - it gives yourself and your company $1 million ea. - Brian Whiffen 
     Bigfoot - Instant Win 
     BoBo - Instant Lose 
     King of the Hill - Gives Player $100 million 
     Cattle Futures - Gives Player $1 Million 
     Powerball - Give company $100 million 
     Slush Fund - Give company $1 million 
     Speed Racer - Trains go double speed 
     AMD103 - All engines are changed into AMD 103s 
     Casey Jones - All other companies' trains crash 
     Show me the trains - Allows the purchase of any Locomotive 
     Viagra - Doubles population 
     Let me in - Opens all territories