Enter one of the following cheat code phrases to activate the corresponding cheat option. Note: Enabling a code will permanently prevent the game from being saved and achievements from being earned.

Lewis and Clark
Enter "YOU GOT YOURSELF A FINE PAIR OF EYES" as a code phrase to unlock all areas.

Decrease Bounty
Enter "THEY SELL SOULS CHEAP HERE" as a code phrase.

Money
Enter "THE ROOT OF ALL EVIL, WE THANK YOU!" as a code phrase to get $500.

Horse
Enter "BEASTS AND MAN TOGETHER" as a code phrase to spawn a horse.

Infinite Horse Stamina
Enter "MAKE HAY WHILE THE SUN SHINES" as a code phrase.

Who?
Enter "HUMILITY BEFORE THE LORD" as a code phrase to become a nobody.

Old School
Enter "THE OLD WAYS IS THE BEST WAYS" as a code phrase to enable the Sepia filter.

NICE. how do i enter these pieces of garbage? also how do i "KlLL" as many people as possible without the law catching up with me? How do I KlLL as many horses as possible? I notice the horses do not "take dumps" is there a reason for this? The horses should probably have full flatulence to generate the kind of authenticity Rockstar was going for. The horses should also pee on people and possible we should be able to do anything with any animal.

I am not sure yet, Am not going to enter them until i beat the game

Rockstar made the horses pretty authentic and realistic, making them have a "brain" they wont do stupid things like running off a cliff edge (although it would be fun)

where exactly do you enter this code?

Pause >> Options >> Cheats

there are more codes out there here are some more:

Lewis and Clark – Enter “YOU GOT YOURSELF A FINE PAIR OF EYES” to unlock all areas

Invincibility – Enter “HE GIVES STRENGTH TO THE WEAK”

Infinite Dead Eye – Enter “I DON’T UNDERSTAND IMNFINITY”

Infinite Ammo – Enter “ABUNDANCE IS EVERYWHERE”

Gun Set 2 – Enter “I’M AN AMERICAN. I NEED GUNS”

Decrease Bounty – Enter “THEY SELL SOULS CHEAP HERE”

Diplomatic Immunity – Enter “I WISH I WORKED FOR UNCLE SAM” to eliminate bounty/wanted level

Money – Enter “THE ROOT OF ALL EVIL, WE THANK YOU” to get $500

Horse – Enter “BEASTS AND MAN TOGETHER” to spawn a horse

Infinite Horse Stamina – Enter “MAKE HAY WHILE THE SUN SHINES”

Sharp Dressed Man – Enter “DON’T YOU LOOK FINE AND DANDY” to unlock the gentleman’s suit
Jack Attack – Enter “OH MY SON, MY BLESSED SON” to change John into Jack, John’s son.

Who? – Enter “HUMILITY BEFORE THE LORD” as a code phrase to become a nobody

Old School – Enter “THE OLD WAYS IS THE BEST WAYS” to enable the Sepia filter

Thanks for posting these, great help

more/clarification:

Activate Sepia Filter “THE OLD WAYS IS THE BEST WAYS”
Become a nobody. HUMILITY BEFORE THE LORD
Decrease Bounty “THEY SELL SOULS CHEAP HERE”
Decrease Bounty THEY SELL SOULS CHEAP HERE
Diplomatic Immunity “I WISH I WORKED FOR UNCLE SAM”
Enable the Sepia filter. THE OLD WAYS IS THE BEST WAYS
Get $500. THE ROOT OF ALL EVIL, WE THANK YOU!
Gun Set 2 “I’M AN AMERICAN. I NEED GUNS”
Infinite ammo “ABUNDANCE IS EVERYWHERE”
Infinite Horse Stamina “MAKE HAY WHILE THE SUN SHINES”
Infinite Horse Stamina MAKE HAY WHILE THE SUN SHINES
Invincibility “HE GIVES STRENGTH TO THE WEAK”
Money($500 on again to get 500 again) “THE ROOT OF ALL EVIL, WE THANK YOU!”
Play As Jack “OH MY SON, MY BLESSED SON”
Spawn a horse. BEASTS AND MAN TOGETHER
Spawn Horse “BEASTS AND MAN TOGETHER”
Unlock all areas “YOU GOT YOURSELF A FINE PAIR OF EYES”
Unlock all areas. YOU GOT YOURSELF A FINE PAIR OF EYES