From the game Super Mario Sunshine for the Nintendo Gamecube
In Delfino Plaza, you can get an unlimited amount of coins. Once you get 100 coins, DON'T grab the shine. Instead, grab a different shine in the Plaza. When the game starts back after you get the shine, you will still have 100 coin. Every time you get 100 coins or more, just grab another shine and the coins will keep adding to the total.
Submitted by: Derek