If you keep tossing a penny over and over it’s likely to land tails up about 51 percent of the time, because the heads side is slightly heavier, meaning the heads is more likely to end up on the bottom.

We call it paper money, but it's really cloth.  American money is a combination of about 75 percent cotton and 25 percent linen.

Cattle are probably the oldest of all forms of money. Using cattle as money dates back thousands of years.  Some cattle were still used as money in parts of Africa in the middle of the 20th century.

Before the days of paper money, Americans traded animal skins, including deer and elk bucks for goods and services. That’s why we use "buck" to describe money.

The Office of Currency Standards will replace a bill if you can present 51 percent of it. If your cash has been burned, torn or otherwise destroyed, they will help you verify and replace that money. They have a listing of instructions on how to pack damaged money and send it to them -  Office of Currency Standards instructions

It costs 6.7 cents to manufacture a dollar bill or any denomination bill.

A stack of 490 paper bills weighs a pound.  A million dollars in one dollar bills would weigh 2,040.8 pounds.  If you used $100 bills it would weigh only 20.4 pounds and fit in a brief case.

The first paper bills printed in the United States were in denominations of 1 cent, 5 cents, 25 cents, and 50 cents. The government was forced to issue these bills because of the hording of coins during the Civil War. Other denominations followed and were called Greenbacks.

The first ten dollar bills had a large Roman numeral X on the back and they were often called a "Dixie" or a "Sawbuck".  For some the X reminded people of the x in Dixie.  For others the x looked like a sawhorse.  Slang for a sawhorse is “Sawbuck".

SOURCE: usgovinfo.about.com