What is the fastest way to get money in GTA San Andreas?
Running taxi missions can get you a small nest egg, which you then want to invest in the horse races - the odds of winning are pretty unrealistic. I seem to remember it being the same odds of success regardless of the odds on the horse.
Save your game before you start, and then bet the max you can on the longest-shot horse. If your horse wins, save, if not, reload your old save. In a couple of runs at this you'll have enough cash to clear the rest of the game easily.
@Ender, I think the casino's kinda decent too (since again, the odds are nowhere near realistic), but the horse races are crazy. You can end up with millions in a half hour or so.
I completed the game to 100% and didn't know there were horse races. Where's the bookmakers?
@ColonelPanic, that's probably better as it's own question, since I'm sure others might want to know. Rest assured they do exist, though :)
Taxi missions are the least profitable (per time) of all missions.