$100 isn’t just $100 and on Yahoo! Finance, New $100 Bills Worth up to $15,000. So what's the catch?
The key is the serial number that appears on the bill. If the serial number is a low number like 00000008, a solid set of numbers like 77777777, or a repeating number like 23232323, or repeaters which are two sets of identical four numbers like 87128712, or a radar number which reads the same forwards or backwards like 43900934, then the note has a value. Bills such as these can have significant value many times the face value.
One thing to keep in mind is the condition of the bill. Don't write on it as it can cause a significant drop in value. As an example, there are a couple of $1 radar notes offered on eBay (EBAY), one in superb condition with a starting bid of $9. The other one was unfortunately stamped with a Where's George stamp in circulated condition, and is currently bidding for $4.99, a tenth of the value.
When you receive a $100 bill from your bank, or for that matter, any currency, even a one dollar bill, check the serial number. If you find a good one, don't fold it or let it get wrinkled. There are plenty of currency and banknote dealers that may be willing to buy it or you can sell it on eBay.