Marvel vs. Capcom

Unlock Shadow Lady as playable character:
Highlight Morrigan at the fighter selection screen, then hit
Up, Right(2 times), Down(4 times), Left(2 times), Up(4 times), Right(2 times),
Left(2 times), Down(2 times), Right(2 times), Down(2 times), Left(2 times),
Up(2 times), Right(2 times), Up(2 times), Left(2 times), Down(5 times).

Unlock Red Venom as playable character:
Highlight Chin-Li at the fighter selection screen, then hit
Right, Down(4 times), Left, Up(4 times), Right(2 times), Down(2 times),
Left(2 times), Down(2 times), Right(2 times), Up(4 times), Left(2 times), Up.

Unlock Orange Hulk as playable character:
Highlight Chin-Li at the fighter selection screen, then hit
Right(2 times), Down(2 times), Left(2 times), Right(2 times), Down(2 times),
Left(2 times), Up(4 times), Down(2 times), Right(2 times), Up(2 times),
Down(4 times), Up(4 times), Left, Up.

Unlock Gold War Machine as playable character:
Highlight Zangief at the fighter selection screen, then hit
Left(2 times), Down(2 times), Right(2 times), Down(2 times), Left(2 times),
Up(4 times), Right(2 times), Left(2 times), Down(4 times), Right(2 times),
Up(2 times), Left(2 times), Down(2 times), Right(2 times), Up(5 times).

Unlock Lilith as playable character:
Highlight Zangief at the fighter selection screen, then hit
Left(2 times), Down(2 times), Right(2 times), Up(2 times), Down(4 times),
Left(2 times), Up(4 times), Right, Left, Down(4 times), Right(2 times),
Up(4 times), Left(2 times), Down(4 times), Right, Down.

Unlock Roll as playable character:
Highlight Zangief at the fighter selection screen, then hit
Left(2 times), Down(2 times), Right(2 times), Down(2 times), Left(2 times),
Up, Right, Up(2 times), Right(2 times).

Unlock Onslaught option:
Unlock all the secret character quick selects.

Change outfits:
Highlight a character at the fighter selection screen, then press A or Y.

Unlock Evil Ryu
Press Down, Down/Back, Back, Fierce Punch.
Note: Need minimum level 1 on you hyper combo bar.

UnlockRed Ryu (Ken times)
Press Down, Down/Back, Back, Medium Punch.
Note: Need minimum level 1 on you hyper combo bar.

Restore normal Ryu
Press Down, Down/Back, Back, Quick Punch.
Note: Need minimum level 1 on you hyper combo bar.

Dual Team attack on Level 3
Press Down, Down/Back, Back + High Punch + High Kick. B
You can contoll both fighters simultaneously for about ten seconds.