"...Man had always assumed that he was more intelligent than dolphins because he had achieved so much – the wheel, New York, wars and so on – whilst all the dolphins had ever done was muck about in the water having a good time. But conversely, the dolphins had always believed that they were far more intelligent than man – for precisely the same reasons."
- From the Hitchhiker's Guide to the Galaxy, by Douglas Adams
As a card carrying marine biologist who doesn't study dolphins or whales, I am obliged to say that they are some of the most uninteresting animals in the sea. But, over at Why Evolution is True, there is a post about dolphins playing with whales that other people might like.