Cheats can be found written around the world of Red Dead Redemption (on walls, in newspapers, etc) but for those who are too lazy to find them all, here is a list in the order the game displays them. Some of these cheats will also work during Undead Nightmare too.
You can enter the following cheat codes in the Cheats Menu under "Options". Enter the entire phrase given below to activate the cheat, punctuation included. Capitalization does not matter. Once a cheat is entered you may toggle them on/off from a master list. If the cheat effect isn't made obvious by it's title, we give a description of it in parenthesis below. Entering cheats disables autosaving and Trophies/Achievements! You can still save at safehouses which adds (*) to the save file in the listing.