Welcome to GTAForums.com.
First of all, this section is for the unmodified version of the game, straight out of the box if you will. For this, all cheats in the game are known and there are no more to be found. The link DarrinPA posted leads you to the modding section which is the place for discussion of all things modding. Note there is a "III Era" which covers San Andreas, Vice City and GTA3 and a "IV Era" which covers GTA IV and its additional downloadable content.
Next thing I would like to address is this - could you please tone down the use of all capital letters and the overuse of smileys. Thanks.