Easy Money
The only thing required is a controller with an auto fire feature. Go to the slots, and choose a machine. It reall doesnt matter but I like the ones with the bigger payout (1000 credits or so).

Set the bets to $5 or $10 bucks and put all of your money into the machine. Youll want to have about 200 credits into the machine, just to be safe. Move your hand to Bet Max Credits, set the A button to auto fire, get a rubberband (or something to hold the A button down) and leave the room for a few hourse. In no time youll have your millions!