The 3rd Birthday Cheats

Free Cheat Unlocking
After you finish the game once you will be allowed to start a new game plus. Start it and you will have the ability to unlock some cheats in the pause cheat menu with your BP. To unlock one or both for free, unlock them and then without saving, reload the new game plus file again. The game will restart with your original BP, but your unlocked cheat will remain unlocked.

Unlockable Costumes
Complete each requirement to unlock the specified Costume (Lightning Custom Costume Available from the 1/1/2011):

Apron Dress Costume: Complete the game on Easy Mode.
Business Suit Costume: Complete the game once on any mode. The Costume is found in the CTI Building in the left hand locker room.
China Dress Costume: Complete the game on Normal Mode.
Knight Armor Costume: Complete the game on Deadly Mode.
Lightning Custom Costume: Complete the game once on any mode and have at least 7 Stamp on Square-Enix Member Site OR Complete the Game 9 times on any Mode.
OD Suit Costume: Complete the game once on any Mode and have at least 1 Stamp on Square-Enix Member Site.
Santa Soldier Costume: Complete the game once on any Mode. You'll find it in Maeda's Base, down the stairs to the lockers, check the left one for the Costume.
Swim Wear Costume: Complete the game on Hard Mode.
Titanium Bunny Costume: Complete the game on Genocide Mode.