SQUARE = Costume 1
X + SQUARE = Costume 2
TRIANGLE = Costume 3
X + TRIANGLE = Costume 4
CIRCLE = Costume 5

Alternate Endings  -  When the endings start, press the following buttons for each character when the view shifts to full-screen: 

Mitsurugi: Use the control pad to dodge Tanegashima's shots, and use Square or Triangle to deliver the fatal blow.+ 
Seung Mina: Hold X and press Left or Right. 
Li Long: Press Square or Triangle repeatedly. 
Taki: Press X. 
Voldo: Press Up and Down rapidly till Soul Edge breaks (you can also change the camera angle while Voldo is speaking to Vercci with the Triangle button) 
Sophitia: Press Right 
Siegfried: Press Triangle 
Rock: Press Triangle 
Hwang: Press Square. 
Cervantes: Press Triangle 

Change Replay View  -  As you are watching your replay, press: 

Triangle: Zoom out
Square: Zoom in
Up: Top View
Down: Horizontal View
Right: Spin Right
Left: Spin Left 

Hidden Level  -  Once you unlock Evil Siegfried and Han Myong a new background will be unlocked 

Namco Voice Trick  -  At the start of the game you will hear a voice say Namco. Hold L1+L2 then press UP for Seung Mina's voice, DOWN for a quick voice or BACK for a normal voice. 
Play as Evil Siegfried  -  Find Siegfried's 8th weapon in Edge Master mode. 
Play as Han Myong  -  After Soul Edge becomes selectable, beat Arcade Mode using Hwang, then Seung Mina immediately afterward. There are conflicting reports whether you must see both endings for these characters or not. 
Play as Sophitia in a Bathing Suit  -  Get every character's 8th weapon in Edge Master mode. 
Play as Sophitia without Armor  -  Find Sophitia's 8th weapon in Edge Master mode. 
Play as Soul Edge  -  To play as Soul Edge, beat Arcade Mode with each character, OR leave the game running for 12 hours. If you pause mid-game, this 'timer' will still continue to run. 

Ultimate Weapon  -  After defeating Cervantes/Soul Edge, your character's Ultimate Weapon will appear in one of the stages that can be reached directly from Spain. If you lose the battle where the Ultimate Weapon was, your character will perform his/her 'loss by time-up' animation on the map screen. If this happens, the Weapon will have moved to one of the stages adjacent to the one you are on, but it will not move to Spain. 

Ultimate Weapon in Arcade Move  -  To use the Ultimate weapons in arcade mode highlight the character you want to be and hold up till a weapon list shows up beside the character. You can also just push select. Now you can choose the Ultimate Weapon or any other weapon in battle.  Note: You must earn the weapons in Edge Master Mode. 

Winning Poses  -  To change your winning pose, press Triangle, Square, Circle or X after you've beat your opponent.