A lot of gold tickets:
While playing, press the combination [Up, Down, Left, Right, Circle, Right, Left, Down, Up, Circle] 4 times, then press Start. You will hear a sound if you entered the code correctly.

All research:
Go to the map screen and press [ Up, Down, Up, Down, Left, Up, Down, Up, Down, Right] 8 times in a row.

Money trick:
When your money is getting a bit low, just save the game, then re-load it. You will find that everyone of your visitors has left the park and within the space of about 5 minutes, at least 50 visitors come back and PAY to get in.

Never lose money cheat:
On the map screen press [Left, Down, Circle, X] 8 times and you will here a signal.

Puzzle money trick:
Get your scientists to research the giant puzzle sideshow, build one and then when somebody starts to play it raise the price to $10,000 and then at the end of that persons go they will pay the $10,000. Its quick and easy and gets you 10k quick