U.S. folks, check your state's "unclaimed property" website to see if you're owed $
Different states have different ways of reporting it, but in general, you'll search for your last name (optionally your first name as well), and you can optionally narrow it down by city. The results are usually shown with the last known mailing address, so you can tell whether it's the right person. (To find the website, just google your state's name and "unclaimed property".)
There's usually a little information about the sort of payment it is, whether the exact amount or "less than $100", and also what company owes the money. It can be anything from a refund on prepaid tolls to having been overcharged at the dentist to having forgotten to change your address with an insurance policy.
Tonight, I found a small amount for myself, my spouse, my father-in-law, and a few others, but found nearly $500 for one of my brothers-in-law! (It's 6-8 different claims, but still, money is money!)
I don't know the process for all states, but for mine, to "claim" the property, I just had to enter my info into the website (name, address, email address, SSN); then I got an email with more details about the particular claim, with a longer form for me to fill out and sign and get notarized. My "under $25" turned out to be $3.xx, so I'm not sure if it's worth taking the time to get it notarized (it certainly wouldn't be worth it if I had to pay for it), but I'm pretty sure my bank does it for free for their customers, so maybe I'll do it when I'm already there.