Atlantis: The Lost Empire Codes -

Unlimited lives:
Hold X + Circle + Square + Right at the title screen. Start the game. Hold L1 + R1 when playing as Milo for unlimited lives. Milo will say "Great" to confirm correct code entry.

FMV sequences:
Get each of the eight Atlantean Symbols in a level to unlock the corresponding FMV sequence under the Movie Viewer option.

Concept Art and Character Models option:
Collect each of the green gems in all levels to unlock the Concept Art and Character Models options in the features menu.