Julie Danielson, a.k.a. Jules of the fabulous Seven Impossible Things Before Breakfast duo, created a lovely annotated Frog Prince/Frog King webpage when she was in library school. These kinds of projects illustrate how useful hypertext links can be in reading material. The "Quiz" feature is no longer active (and I'm really curious now to find out what it originally entailed) but just about everything else should be in place for you to find out the intricacies of this story that often begins Grimms' fairy tale collections.
I once wrote a poem about the Frog Prince. Reading it gave my friends the feeling of claustrophobia, which was a accurate assessment of how I felt about the story. There's lots to study with layers of meaning (different layers, depending upon who's interpreting the story), but everyone except the Frog Prince's servant, Iron Henry, is pretty irritating to the point of being stifling. The princess is spoiled, the frog is pushy, and the king tells the princess that she has to keep her promise when the reader gets the feeling the princess is too young to be involved in a binding contract. Also, who started the rumor that the princess kissed the frog? At the climax of the story, what frees the frog from his enchantment is not an act of love but one of violence. This is no Beauty and the Beast.