Someone recommended the following links
Monstropedia
Mythical Creatures List, Mythical Creatures A-Z
Monstropedia
Mythical Creatures List, Mythical Creatures A-Z
I just pull out my Monster Manual from D&D and modify the monsters in there.
Ohhh, I was going to recommend Monstropedia!
One other great source for monsters: any book on prehistoric creatures. What better place to look for muse than science and history?