Here is a short list of the Super Mario Sunshine Gecko Codes I have made.
100 Coins on D-Pad Up
Nozzle Selector (2nd Nozzle)
Description:
Changes the 2nd Nozzle to the selected nozzle based on button combination.
X + D-Pad Left: Hover Nozzle
X + D-Pad Right: Rocket Nozzle
X + D-Pad Down: Turbo Nozzle
More codes are coming soon and as always, happy cheating!
100 Coins on D-Pad Up
Need to find the file again 
Nozzle Selector (2nd Nozzle)
Code:
28404454 00000401
04269F50 3BE00004
28404454 00000404
04269F50 3BE00005
28404454 00000402
04269F50 3BE00001Description:
Changes the 2nd Nozzle to the selected nozzle based on button combination.
X + D-Pad Left: Hover Nozzle
X + D-Pad Right: Rocket Nozzle
X + D-Pad Down: Turbo Nozzle
More codes are coming soon and as always, happy cheating!
