Cheat Codes
Unlock The Dressing Room:
Finish one offline story, and use it once. Then complete the second offline story to permenently unlock it.
Billy Hatcher Preview:
From the title screen, hold G + B on the keyboard.
Unlock Bonus Cards:
Put in a memory card that contains a save game from any other Sonic Team game, and you'll get some bonus cards.
Sonic Team Game: Bonus Cards Unlocked
Sonic Heroes:
Beat, Halloween Rappy, Sonic Knuckle
Billy Hatcher:
Clippen
Sonic Mega Collection:
Madam's Umbrella
Phantasy Star Online Episodes I & II:
Nano Dragon
Sonic Adventure 2 Battle:
Rage
Sonic Adventure DX:
Sange