I have one about my friend:-
She was living with a few girls in a flat when she was at uni. The flat backed onto a large bit of unused ground, which most people living in the block or visting folk in the block used, as it was a bit of a shortcut.
Anyway, one night after being out for a few drinks, she was going back to the flat to meet up with her DP - they were walking through the unused bit of land and she dropped her keys - bent down to pick them up and there was this box on the ground. She picked it up and opened it - inside was a diamond ring.
Her friends tried to convince her to keep it, but she didn't think that was right, so the next morning she took it to the local police station. The policeman helpfully told her that if no-one claimed it in 6months, she would get to keep it.
About 2months later, her DP takes her on a romantic walk around the city and stops, gets down on one kneee - yep, you've guessed it - he proposed to her. He opened the box to show her the ring - and guess what - it was the ring she found on her way home.
Turns out he was going to propose to her that night, but lost the ring on the way from his flat (he cycled from just over a mile away) He spent the whole night trying to find the ring, retracing his steps, but couldn't. He ended up going to the police station a few days later - with no hope of recovering the ring, and was amazed that someone had handed it in.
She never told him about finding the ring.
She got to keep it after all