Debt, I know I know its morally dubious, but yes, debt, a garunteed return on your investment (though the timeframe is variable depending on what countries debt you buy into) typically from what I've read, you'll make about 40% on whatever you put in.
American Debt atm looks to be a good place to start, since theres a lot of it and a reletively stable system of governance in place to garuntee a return.
Dunno however how you'd get in touch with a debt trader though.