The correct think to do is turn it in to the police and if it is not claimed in a certain amount of time you get it. The only problem with that is if the police officer could be end up talking it and you may never know it wasn't claimed.
turn it over to the fuzz and if not claimed in whatever time limit they have then its mine. I might take out an add in the paper with some of the money - let it run for a week - this way my mind is clear when I am stuffing 1 dollar bills into strippers undies.