Devil May Cry 3: Dante's Awakening (PS2)

Get Everything
At the start menu hold L1 + L2 + R1 + R2 then rotate the Left Analog-stick. You will here a voice say "Devil May Cry" and all modes, costumes, and galleries will be unlocked.
(Note: this code verified for U.S. version of the game only)

Unlockable Modes
To unlock Hard Mode beat Normal Mode
To unlock Dante Must Die beat Hard Mode
To unlock Heaven or Hell beat Dante Must die

Alternate Ending
Kill 100 enemies during the credits to get a different ending screen.

Unlockable Characters
Press R1 or L1 at the mission select screen to get different characters.

Beat the game on easy for shirtless Dante
Beat the game on normal for Devil May Cry 1 Dante
Beat the game on hard for shirtless Devil May Cray 1 Dante
Beat the game on hard to unlock the Legendary Dark Knight
Beat the game on hard to unlock Sparda

Infinite Devil Trigger
Beat 'Dante must Die' mode to unlock the Devil Trigger.

Hint: Weapon Reloading
Tap L2 after firing a slow-to-reload weapon (like the shotgun) and flick it back to fire it again. It is a little bit faster than waiting for the weapon to reload as per normal.