The floor. Lots of people drop pennies and small coins all the time. I've found all sorts of coins on the floor. I pick up whatever I find and usually, living in the UK, I put the 1p, 2p, 5p,10p, 20p, £1 (I missed out 50p and £2 because I have never found them on the floor) in separate pots and wait for them to build up.
Coin lockers...telephones...broken ticket machines....all good places to look. And you'll be surprised blocked drains. I've found a £5 note down a drain once. £20 in Boots: gave it in, got it about 6 weeks later.
I was thinking about writing a separate post about this but: there were some young lads playing football with a penny in London and I thought any minute now they are going to leave it alone. They did and I rescued it and took it home and it is probably still in my penny pot, scratched, scuffed, and ruined but it is my penny now...and I can take that to the bank. Does anyone else turn to the sound of where lots of money has been dropped...eyes darting about looking for the coins? Anyone think about rescuing obliterated coins etc? You know the quirks...in quirkiness of coin collecting?