If I was a game designer, I'd bookmark the Encyclopedia of Life project. Encyclopedia of Life is an ambitious taxonomy project, hoping to catalogue every species on Earth into a single index. The variety of life in our world is truly endless, and this is a great way to get ideas for creature design... not just visual design, but behaviors and abilities.
I've mentioned Blogger Play and TerraGalleria before. Studying reality is a great way to find inspiration for all aspects of game design.