When we were much younger, Dylan and I would dream up things we could do to make money with as little effort as possible. The goal is what I call the "Frictionless Scam." That is, you want no contact with the client nor with the police. So it has to be legal and something that doesn't require the client in the room with you. You want to cash the check, hand over the product and everyone walks away happy.
A good example would be computer-generated astrology or biorythm charts. Feed some random or nearly random numbers into a program, print out the chart, mail it to client and cash the check.
Another silly idea I had while stuck in a traffic years back was auditing vehicles for possession by a ghost or extraterestrial or something. Which would involve a box with blinkenlights and dials. Then you create a certificat that guarantees the vehicle is ghost-free. Now given that ghost don't exist, you would be pretty safe from a legal stand-point. But the fact that you have to do a show and dance for the customer means this isn't a frictionless scam.
Neal Stephenson came up with a great Frictionless Scam: plug an Eliza-like chatterbox into voice synth and voice recognition software to build a phone sex service. "Is it because of your massively erect penis that you came to see me?" "Enough about me, what are you wearing?" "Do my large melons excite you?" "What does this tell you?" (If you haven't played with an Eliza, you might not get the previous joke.) Of course, neither voice synth nor voice recog are up to the point where we can do this and you still need a large server somewhere with an expensive T1 to pull it off. What's more, in 2012 it would have to be a 3d generated web cam stream.
Now it seems that Print On Demand and Amazon have created another near fricionlessscam. Take some Wikipedia articles, edit them into a book, sell book on Amazon. And thanks to PoD, you only have to print the book if/when you actually sell it. And given that Wikipedia has good markup, you can pretty much automate the conversion from Wiki to PDF that gets sent to the On Demand printer.