I found over $800 in an aisle at a Walmart during Christmas season one year. I gave it to the store manager - I hope it got back to its owner.
I found a gold wedding band in the street one spring. It turned out to be a neighbor's ring. We had a huge snowstorm a few months previous and it went flying off of his hand when he was shoveling and they hadn't been able to find it with all of the snow.
Probably the most precious...last summer I found two children, ages 6 and 8, wandering on the beach. It gets pretty crowded, so it is fairly routine for kids get separated from their parents there. Usually you can spot the parents in an instant, but in this case they just didn't look "right" to me. So, I went over to check in with them and see if I could help. Another adult came over and we started to look. I could tell fairly quickly that the parents weren't around, so I called the police. It turned out that they had been lost for several hours, wandering the beach, with the authorities looking for them. They had been at a birthday party over 4 miles away down the beach, and had wandered away while their parents were helping to clean up. The ocean was really rough that day, and I still get sick to my stomach when I think about those kids walking along the shore for that long.