Common Magical Creatures -
Banshee - Centaur - Chimera - Dragon - Dwarf - Elf - Fairy - Genii (Genie) - Gnome - Goblin - Griffin - Human - Hydra - Kobold - Leprechaun - Mermaids / Mermen - Minotaur - Nix - Nymph - Ogre - Phoenix - Pixy - Pooka - Poltergeist - Satyr - Sorceress - Sphinx - Sprite - Three-Headed Jackal - Titans / Giants - Troll - Unicorn - Vampire - Werewolf - Winged horse - Wizard

Rules of Magic -
When dealing with magic in a book, an author must realize that there are certain boundaries that must be considered in order to create a believable tale. For instance, if a wizard is able to heal anything, he must be able to do so througout the story.

Recommended Books -
Tough Guide to Fantasyland, by Diana Wynne Jones
Time Travel, by Paul J. Nahin
The Writer's Complete Fantasy Reference, by Writer's Digest