If you have Seasons save up for the Money Tree reward....it yields 8,000 simoleons from the get go and that amount increases as you improve the quality of the plant.
Choosing the Fabulously Wealthy aspiration pays off very well once you achieve it too, as your sim will get an investment payment every week. Right now my sim couple (who doesn't work) is receiving 46,000 simoleons daily from four money trees, and each of them receives around 120,000 simoleons weekly for their investment payments. It did take SOME time to get here, but not as much as it would to try to go up the ranks of a career. Needless to say their wealth is growing exponentially at this point.