Airblade

Level select:
Press Start to pause game play, then press Square, Circle, Triangle + Square, Square, Circle, Start.

Invincibility:
Press Start to pause game play, then press Square, Circle, Triangle + X, Square, Circle, Start.

Pass through objects:
Press Start to pause game play, then press Square, Circle, Square + Circle, Square, Circle, Start.

J. J. Sawyer:
Successfully complete the game with an "S" rank in all levels.
alistair2001.

Naomi:
Successfully complete the Downtown level with a "B" rank.
alistair2001.

Oscar:
Successfully complete the game with an "A" rank in all levels.
alistair2001.

The Insider:
Successfully complete the Storage level with a "B" rank.
alistair2001.

Stunt attack mode:
Successfully complete the game in story mode.
alistair2001.

Alternate costumes:
Complete one of the following tasks to unlock a third costume for the indicated character.
alistair2001.

Ethan costume C: Successfully complete stunt attack mode.
Kat costume C: Successfully complete score attack mode with high scores in all levels.

Hint: Corporate HQ: Stop on cable car:
Select Ethan and enter stunt mode. Play the Corporate HQ level and go to the last cable car. When grinding it, press R1 and you will stop on it.
Bryce Povey.

Glitch: Fall through door:
Unlock Naomi, select freestyle mode and go to level three (Industrial). At the end of the level, go off the left ramp from the exit (at the search lights). Avoid the big pipes, use Speed and Boost Jump, and you should fall through the door and float in darkness.
paulacollinsburke.

Glitch: Stuck on wall (demo version):
In the first level near the pile of boxes out the back of the Chinese shop, go up the wall and land on the wall. You will not fall down and can as many stunts as desired. You can stay there and do stunts up to and after the time has stopped.
Hopes2plus3.