In single player mode, press ESC to pause game and type:
no more road splats - Infinite lives
show me more zones please - All zones
way too hard for the likes of me - All levels
Pause the game, press Caps Lock and type: "Time flies when your having trouble" Invincibility
To get invinsibility, pause the game and type, "I am the king of the world" you will hear a noise and you cannot die, if you fall off an edge, you will be placed back up by a white angel frog.
Thanks to Revolution readers J.T. Shaver, Max Haesler, and Ron & Michelle Coffman!