Infinite Ammo:
     To  get infinite ammo for all of your guns, pause the game and go
to the map screen and press X(2), O(2) and Square.

Hard mode:
     At  the  title  screen, highlight the One Player option and press
Square + Circle + L1 + R2 + Select + Up + X.

End Mission:
     Pause  the game, highlight the Map option, then hold Right + L2 +
R2 + Circle + Square + X. Enter the options screen and select Cheats.

Super Agent mode:
     Pause the game, highlight the Weaponry option, then hold Select +
L2 + Circle + Square + X. Enter the options screen and select Cheats.

Movie Theatre:
     Pause  the game, highlight the Briefing option, then hold Right +
L1 + R2 + Circle + X. Enter the options screen and select Cheats

2-Player Arenas and Characters:
     There  are  10  hidden items that must be picked up in the single
player mode to open the 10 locked 2 player arenas. There are 20 Arenas
in  all.  Some  of  these  hidden  items,  such as the Binoculars, are
inventory  items  and  others  such as the Girly Mag and Dirty Laundry
cannot  be seen in your inventory when picked up. There are a total of
28  characters, but only 10 of them are initially available. The other
18 characters are unlocked through 2 secrets in the latter half of the
game. What they are is unclear at this time.

Ammo and Gun:
(Gun later revealed in level)
     In  the  first  level  (the Rockies), there is a tunnel where the
water  fall  is.  Go on the side with the flare thing and go jump over
the  cliff, dont worry, he automatically jumps over. When you do that,
back  up  so you hang off, Then drop down. Go to the end of the tunnel
which  there  are  no  guys  in.  Get  300 ammo for the HK11. It is an
automatic  silenced  sniper rifle.(Make sure you are on the other side
that the fire is not on!)

Super Agent mode:
     Pause  the  game, highlight the "Weaponry" option, then hold L2 +
Select + Circle + Square + X (simultaneously). If you entered the code
correctly,  you  will hear a sound. Then, enter the options screen and
choose the "Cheats" selection.

Caves multi-player stage:
     Find the binoculars in the Colorado Interstate 70 level. They are
located  behind  the  first  closed  door on your left that you reach.
Press Triangle to open the door. This reveals a passage. Go left, open
another door, and enter the room. The box containing the binoculars is
in this room.

Pharcon Site multi-player stage:
     Find  the  girlie magazine in the Pharcon Lab, after you taze the
guards. It is located after you go through the Mars exhibit.

Bunker multi-player stage:
     Find  the  PK-102  in  the Moscow Streets level. There is a point
where two cars will try to run you over at the same time, and you have
to  leap  and grab a pole above you to avoid them. After this happens,
drop down, and go back and search the two newly crashed cars. Face the
tail ends of the cars. The car on the right has the PK-102 inside. The
cars  are  on  fire, so search carefully. Additionally, after the cars
crash  an  enemy  will get out of each car. At least one of them has a
M-79 grenade launcher.

Additional multi-player characters:
     Find  the  M-79 grenade launcher on the second to last level (New
York  Sewers)  to  unlock the following seven multi-player characters:
Ninja  Gabe,  Scuba  Lian,  Unit  1  (armored trooper from the Bio-Lab
Escape level), Dr. Elsa Weissinger, Uri Gregorov, Lawrence Mujari, and
SWAT  officer  (helped  in the New York Slums level). The M-79 is near
the  end  of  the  level  (in the parking garage). Near the top of the
stairs  is  an open doorway into the parking garage, where a black van
is  driving  past.  Instead of exiting the stairwell at that location,
keep  climbing  up  the  stairs.  There will be five Agency operatives
scattered  on  the landings above armed with silenced HK-5s, grenades,
and  M-79s.  Use  the  M-79  to clear them out. The M-79 is on the top
landing.

Killing Chance:
     First  of  all,  he is wearing full body armor so you cant attack
him  with  any of your current weapons. Ok now when you start the game
head  out  of  the right door and roll and run towards the helicopter.
Once  you  get  there  you  should  see  an ammo box with the UAS12 or
something  like  that. (A gas-grenade type of gun). After you get that
roll under the helicopter's back end (being careful not to go into the
spinning  blades.) Now if you have been shot by Chance run over to the
opposite  side  of the helicopter and grab the flak jacket in the ammo
box.  By  the time you have completed this, Chance probably has rolled
under  the  helicopter  after you. Take the grenade type gun and start
shooting  him  into  the  chest,  making  sure  he is in line with the
rotating blades on the back end of the copter.

Extra Gun:
     In  the  first  level  there is an easier way to get the H11 from
under  the waterfall. Just simply get as close to the edge as you can,
and roll in by using the Circle button.

Sniper rifle on first level:
     On  the  first  level  you  can  control where you land with your
parashoot  (or  however  you  spell  it)  now  control yourself in the
direction  of the 3 men and the flares try and land yourself on top or
so  your  hanging off of the cliff right above them and there it is in
the ammo box.

Air Taser in level 1:
     When  you  go  to  the  highest  point  on  level one and get the
tansponder to work. When you areon your way back look to your left and
and  go to the edge and crawl down to hang on to the cliff (press walk
when going to the cliff to crawl down and hang) move left and you will
find a box which has the air taser.

Extra Multiplayer Level:
DC Park Multiplayer Arena
     In  the  third  last level of the game, Slums, play through for a
while  until  the  part  where you have to help the swat team kill the
snipers. When you get there, there is a building with smoke rising out
of  the  entrance,  enter the building. When you enter carefully go up
the  ramp  inside  the  building  until you reach what looks to be old
washing  machines. After a radio signal, go to the last machine in the
row.  Press  triangle  to  pick  up  the  dirty  laundry. You have now
unlocked DC park.

Here are the multiplayer characters you can unlock:
SF1 Earned Characters:
Anton Girdeux
Jorge Marcos
Jonathon Phagen
Erich Rhoemer
Evil Scientist
Vladimir Gabrek 

SF2 Earned Characters:
Unit One
Dr. Elsa Weissinger
Ninja Gabe
Uri Gregorov
Lawrence Mujari
Scuba Lian
Swat Officer