Street Fighter 3

Full pause screen -
Press X + Y, while paused the gameplay.

Unlock Gouki (Akuma) as playable character:
Go to the fighter selection screen, highlight characters of Sean
and push Up.

Unlock Shin Gouki (Akuma) as playable character:
Play through SF 3: Double Impact and defeat the last Boss without
loosing a single rounds. Reach a perfect at least 3 times.
After, beat Gouki with perfect or super arts to fight with Shin Gouki.
Beat Shin Gouki to unlock him at the fighter selection screeen.
Hold Start and press any kick button to play with him.

Unlock Gill as playable character:
Finish SF 3 or SF 3: Double Impact in any difficulty level.
After go to the gfighter selection screen, highlight characters of Sean
and press Up, Up.

Unlock Yang as playable character:
Go to the fighter selection screen, highlight characters of Yun and
press any Kick button.

Unlock Extra options:
Play any game and hold L + R on the options screeen.
Keep held L + R, the new options appear at the end of the code.

After highlight the "Game Option" and press the following button combination:
Left, Left, X, X, Right, Right.

After highlight the "Button Config" and press the following button combination:
Left, Left, Y, Y, Right, Right.

After highlight the "Screen Adjust" and press the following button combination:
Left, Left, X, Y, Right, Right.

After highlight the "Sound" and press the following button combination:
Left, Left, Y, X, Right, Right.

If entered the codes correctly, the "Extra Options" will be unlocked.