BOOKS
The Dictionary of Classical Mythology. John Edward Zimmerman. -- Exactly what the title says. This is a dictionary of Greek and Roman mythology. It's a good, straightforward reference.
The Dictionary of Mythology: An A-Z of Themes, Legends and Heroes. J.A. Coleman -- A great first-stop reference when looking up all things mythology. This covers a wonderfully wide range of cultures and mythologies. It is, however, a dictionary and not an encyclopedia, so you won't get in-depth entries.
The World Almanac Book of the Strange -- The original book of strange things, it was one of my first references on weird.
World Mythology: An Anthology of the Great Myths and Epics. Donna Rosenberg -- A good survey of mythologies from some of the major cultures around the world. Rather than summarize these myths, this book recounts pivotal tales like the Iliad, Enuma Elish, and several creation myths.
ONLINE
Encylopedia Mythica -- One of the first sites I go to when I'm looking something up. Sometimes the entries are on the sparse side, but the information is good.
Monstrous.com -- The "largest network of websites about monsters" focused on mythological and supernatural creatures. Contains articles, pictures, and videos. It's a bit chaotic, but one can't deny the scope of information.
Myth Index -- As the name states, this is an incredibly extensive index of names from Greek (and Roman) mythology.
Theoi Project -- A site dedicated to Greek mythology, particularly in regards to classical literature and art: "The aim of the project is to provide a comprehensive, free reference guide to the gods (theoi), spirits (daimones), fabulous creatures (theres) and heroes of ancient Greek mythology and religion."
