I spent every free moment devouring every dolphin book I could find, and I quickly learned how little most people actually know about these charismatic creatures. (Among many others, I highly recommend "To Touch a Wild Dolphin" by Rachel Smolker.)
I was also excited to learn that--like humans--dolphins often enjoying engaging in play for no other reason except that it probably feels good and strengthens social bonds. Here's a great YouTube video taken in Jeffreys Bay, South Africa, that depicts an enthusiastic pod of surfing dolphins. Enjoy!