No money cheat codes have been released on the GTA websites, and most of the websites say that such codes do not exist. However, some internet pages claim that the code "666555666" (entered anywhere) provides unlimited extra money.
An alternative way to get extra money in GTA4 is the so-called "ATM trick". To perform the trick, you need to kill somebody who just came from a cash machine and block the roads in the area. The ambulance will not be able to get through, and you will be able to repeatedly pick up the cash from the dead body. According to Video Games Blogger, "The more people you've killed, the faster this goes."