- The story of Demeter and Persephone
- Odin's quest for the Runes (from the Hávamál)
- Inanna's descent to the Underworld
- The story of Orpheus (see also painting by Corot)
- Robin Hood
- King Arthur and the Holy Grail (more)
- The Mabinogion (especially the stories of Pwyll and Rhiannon and Gwydion)
- The Gnostic version of the Garden of Eden story
- The Wild Hunt
They should also know the myths of their own folk heroes (e.g. Tam Lin and Thomas the Rhymer in Scotland, Owain Glyndwr in Wales, El Cid in Spain, Jeanne d'Arc in France, Tannhäuser and Herman in Germany, Ctirad and Šarka for Czechs, High John the Conqueror for African Americans, etc etc.) I have included Robin Hood and King Arthur in the main list because ideas relating to them have fed into Wiccan ideas and philosophy.
Edit: after discussion with friends, I feel bound to point out that when I say should, I mean "you owe it to yourself if you want to be a quality witch". Knowing about the things on the list above will help when writing and participating in rituals, as then you will get more out of them.