This isn't really a cheat, so I'll say it. I use rich sims for their money. Whenever my sim meets someone they love I have that sims entire family move in and then I move out the excess sims after selling all their possessions. I only do it for sims they love though. I've done it a few times now in the game I'm currently playing and I'm up to $800,000 simoleons. I don't even know why I make my sims work anymore.
Another one is turning sims that are at the top of their careers into vampires.