Loan sharking is very lucrative, but you can get far more vig if you offer "payday loans" in certain states, and it's completely legit.

Drug dealing is way too dangerous and carries double digit sentences.

Counterfeiting used to be a sure-fire, high-yield racket, but modern technology makes it almost impossible to run off phony money that could pass muster at even a convenience store counter.

Speaking of counterfeiting: Our local paper here once ran an article headlined: "Police Warn of Counterfeiting". The story said a guy tried to pass a bad bill at a McDonald's. "Police described the fraudulent bill as 'a poor quality Xerox'--the front was a $50, the back was a $20." I guess the guy was hedging his bets with the cashier: "Uh, can you gimme change for a fifty? No? How about a twenty?"