Here's a puzzle I just heard about today. I found it enjoyable.
We have the following people on one side of a river: Policeman, Criminal, Parent A, Parent A's two children, Parent B, and Parent B's two children. There is a 2-person raft available for use. Only the Policeman and the two Parents know how to control the raft. The goal is to move all the people to the other side of the river.
Here are additional constraints:
Criminal cannot be with anyone without the presence of the Policeman.
Parent A cannot be with any of Parent B's children without the presence of Parent B.
Parent B cannot be with any of Parent A's children without the presence of Parent A.