The U.S. Treasury
Buying a U.S. savings bond was considered a patriotic act during World War II and has always been a solid, if conservative, investment idea. Savings bonds and other securities are sold by the U.S. Treasury to pay off the nation's debts. Treasury bonds pay relatively low interest rates and take up to 30 years to mature, but they are considered one of the safest investments around — unless you never cash them in.
The U.S. Treasury maintains a searchable database called Treasury Hunt (even bureaucrats have a sense of humor) that can help you identify lost or mature savings bonds. All you have to do is plug in your Social Security number or the number associated with the bond. Keep in mind that the online service only works for Series E bonds issued 1974 or later and Series EE bonds issued 1980 or later.