Pause the game and Enter these codes:

Invisibility:
Press R1, L1, L1, R2, L1, L1, L2.

Light Cars:
Press L1, R1, R1, L2, R2, R2.

Zero Gravity:
R1, R2, R1, R2, Up, Up, Up.

Decrease Ttime Warp:
R2, L2, L1, R1, Left, Left, Left.

Increase Time Warp:
R1, L1, L2, R2, Right, Right Right.

Wizard of Oz Mode:
R1, R2, R1, R2, Up, Up, Up a sound should confirm the cheat.

Hints

Use A Midnight Club Car:
First play Midnight Club and create a save. Now, play Smuggler's Run. Instead of loading the Smuggler's Run save, load the Midnight Club save. You'll now be able to use a car from Midnight Club.

Thanks to Revolution readers Eric R. Barbre, Rob and Matt Ezarik!