NOTE: There have been many problems reported with the cheats below. Please let us know if they work for you. Thanks.

Where's Ronaldo?:
In the game Ronaldo can be found on the "Inter Milan" team known as player A. Calcio
Thanks to gst

Infinite Money:
Goto the "Team Edit" screen and enter the following:
L1 L2 R2 R1 circle x square triangle start select
Thanks to jthomas

NOTE: The cheats below have not been tested, please let us know if it works for you. Thanks.
World's Best 25 Players
Goto Team Management and then Transfers and enter:
L2,L1,R2,R1,SQUARE,TRIANGLE,UP,DOWN,LEFT,RIGHT,SELECT
You will hear a Plop sound if entered correctly.
Thanks to ALAN HOUSTON AND BOB SCOTT

Infinite Player Attributes:
Go to the Player Edit then go into the player attributes and press L1 L2 R1 R2 square square d-up circle. If this is successful you will hear the crowd shout GOAL