You rarely get as big a no-brainer investment possibility as the United States Postal Service is offering today. Right now—Saturday—if you walk into a Post Office, a "forever" stamp entitling you to mail a letter will cost 46 cents. Starting on Monday, it will cost 49 cents.
That's a 6.5 percent return on investment for buying stamps today. And while nothing in life is totally risk free, it's about as close to a sure thing as you're going to find. And it's an especially low-risk investment for something with such a high return! Bringing this investment to scale in order to make real money off of it would be very challenging. But if you don't already have a bunch of stamps lying around the house, you should definitely get some today. These kind of opportunities simply don't come along all that often.