A large electronic box that steals all your money. Very hard
"Hey Man you wanna go to the movies?"
"After i beat this level"
*2 hours later*
"I just spent $200 but i finally beat this level"
A sizable video game machine, ranging from cocktail-table size (the size of your average coffee table,) to monstrous cockpit-style units.
Owning a few of these bad boys could potentially make you rich -- with having to do little or no actual work. All you do is strategically place them in public locales, and empty out the cash box, repeatedly... Sure, you'll have to pay the business owner a percentage, but you'll still make a shitload of money.
I found me a VERY used arcade machine for only $30 dollars. I just gotta fix it up a little bit, put it in the local beer joint, and I'll have a decent secondary income to go along with my paltry grocery store paycheck...