The Dapper Dans are a barbershop quartet that has been performing at Disneyland since 1959. They also perform at Disney World and other international Disney locations. You can usually find them around Main Street in Disneyland, and sometimes they are on a Schwinn four-seater ordered especially by Walt Disney.
Even though I would not usually stop for a barbershop quartet, these guys kinda rock. It seems very difficult to become a member of the Dapper Dan and once a member joins, he sticks around until retirement or death. One of the quartets in Disneyland was together for ten years!
Here is a video of a Dapper Dan performance of Do You Remember When.