A fine art search engine great for tracking down paintings that contain mythological references. Greek and Roman mythology are the most popular subjects for fine art.
On this blog run by another mythology teacher, you can find many amusing posts relating ancient mythologies to popular culture. I also love that it's named after Bubo, that obnoxious metal owl from the original Clash of the Titans.
If teach and you've never heard of the National Writing Project, you should definitely check it out! Ozarks Writing Project is the particular branch that encouraged me to start publishing my mythology materials.
Ye Olde guide to the beasts of the world. To the people of the Middle Ages even common beasts were fantastical. This site has changed an actual medieval bestiary it an online, searchable format. Now animal lore from centuries ago is only a mouse click away.