Easy Gold Ticket:
To get a Gold Ticket, you must play the main game. When building your park, put the rides or shops as close as possible. Then, train the staff up to level 5. Then, put rides on research, and so on.

To do these cheats go to the select park screen or "MAP".

Get 200 Gold Tickets

Press up, down, right, left, down, up, circle
You must do this cheat 4 times in a row.

Everything Free

Press left, down, X, O
You must do it 8 times in a row.

Get All Research Done
Press up, down, up, down, left, up, down, up, down, right
 You must do this cheat 8 times in a row.

Gold Tickets
If you have the video camera,  go into 1st person mod, go to the sideshow and press the play button.  if you beat the sideshow you'll win a gold ticket. This only happens the first time.