Yokai are strange fantastical creatures/spirits based in Japanese folklore. There is a wide assortment of them, some good, some bad. They generally have a direct resemblance to certain animals. Many artists have depicted Yokai over the past several hundred years. Hayao Miyazaki's recent film "Spirited Away" included a lot of Yokai mythos. Linked here are many galleries showing Yokai in sculpted, painted and drawn variations. I suggest tracking down the 3 films based on Yokai from the late 60's titled "Spook Warfare, 100 Monsters and Along With Ghosts." And 2006 is a good year to be a Yokai fan as Takashi Miike's latest film titled "The Big Spook War" is due out, which is based directly on the Yokai mythology. You can find the trailer for it at this site.
Most of these galleries are in Japanese but the navigation is usually straight forward.
12th Gallery - over 100 Yokai pics in this one, check it out.
13th Gallery - Gallery of creatures from a Yokai inspired videogame.