Final Tornado
Description: The final tornado that threatens Metropolis is easy to figure out after a few tries.
How to: You have to save about 3 or 4 citizens in various places so do that first.
Now you have to go and put out a couple of building fires. Try using the SUPER DUPER Breath. One blow will snuff the fires. Then Superman will say something corny -- along the lines of, "I have to try one more time". He'll automatically fly into the tornado and here's where the encounter gets simple.
When the tornado turns blue inside, use your heat vision and when the tornado turns red, use your ice breath.

Bizarro
Description: You can find the cheat code on the Superman Returns DVD.
How to: At the menu, enter UP, RIGHT, DOWN, RIGHT, UP, LEFT, DOWN, RIGHT, UP. Once entered, fly to the top of the GNN building.

Cheats
Description: Enter these cheat codes while in the Fortress of Solitude. To get there, hit BACK while in the game to access the map, then press YELLOW to access the Fortress. "Supe R Man" cannot access the fortress while there are enemies around, only when you're in free fly mode, so go kick some ass.

Using cheats will not earn you any achievements while they are active (although one achievement (specifically for entering a cheat) will unlock as soon as the first code is entered). You still have to go out through the city and find your lost/hidden kittens and mini-games.

Unlock all Unlockables (not Collectibles) :LEFT, UP, RIGHT, DOWN, YELLOW, BLUE, YELLOW, UP, RIGHT, BLUE

Unending Stamina :UP, UP, DOWN, DOWN, LEFT, RIGHT, LEFT, RIGHT, YELLOW, BLUE

Metropolis Is Indestructable, Like Tokyo :YELLOW, RIGHT, YELLOW, RIGHT, UP, LEFT, RIGHT, YELLOW

All Power-Ups Available :LEFT, YELLOW, RIGHT, BLUE, DOWN, YELLOW, UP, DOWN, BLUE, YELLOW, BLUE

Pod Suit
How to unlock: You have to defeat Bizarro.

Infinite Health
. . . Y, RIGHT, Y, RIGHT, UP, LEFT, RIGHT, Y