For online games creating cheats is incredibly difficult. You can learn how to manipulate packets (information sent between you and the website) in certain majors in college, but they make you take an ethics class so you don't go around messing with the world haha!
Your best bet to get CityVille cheats would be to find a bug and exploit it.
Do not trust anybody on the internet saying they have a cash generator... ITS NOT TRUE and most likely contains spyware!!!