House of The Dead 2
Bonus Level:
     Beat the first training mission.

Ready 2 Rumble
Get Rumble gloves:
     First hit your opponent to spell out the word "Rumble". Then push
the two top trigger buttons at the same time.

Champ Car Racing
Rainy weather:
     On  the  Transmission  Select  screen,  hold  L + R + Down on the
D-pad,  choose  your  transmission, continue to hold until game starts
for rainy weather.

Powerstone
Extra Arena:
     Remember  the  arena  you  can  play  in  one-player  mode but is
normally   unaccessible   in  two-player?  Simple.  When  you  play  a
two-player game, at the end of the match, hold all four action buttons
and  press  start  to  return  to  the title screen. Then go back to 2
Player mode and have someone pick Gunrock as a character. Now when the
stage  select  screen  pops up, Voldo should be accessible right away,
BUT  DO  NOT  MOVE  THE CONTROLLER EXCEPT TO PRESS A! Or else you will
move to the normal 2 arenas and can't pick the hidden one.

Powerstone
Replay:
     If  you  win  or lose while playing Power Stone, just press all 4
action buttons at the same time and then start. This will bring you to
the beginning screen of Power Stone instead of the Generator Disc Menu

Flag To Flag
Cloudy weather:
     Highlight  "Automatic"  or "Manual" at the transmission selection
screen. Then, hold L + R + Up and press A. Continue to hold L + R + Up
until the track completes loading.