How do you find out the current value of any US coin or bill?

It depends on when the money was made. Modern U.S. coins and bills are basically just worth face value. Many older coins and bills however are worth more because they contain a precious metal such as gold or silver, and/or are in demand by collectors.

There are numerous guidebooks available on-line and in libraries that can help determine a piece's collector value - Coin Prices magazine, Banknote Reporter, and so on are good print sources.

However, as with any collectible you have to know what you are looking at, so if you have older coins are bills you need to do some research on things such as mint marks (for coins), series dates (for bills), and condition grading.