I would love to hear about everyone's favorite Filk and Fantasy or mythology based songs!
Personally I love Heather Dale's Avalon Album (especially The Trial of Lancelot) and her songs One of Us and Joan and also, Threes (the one based on Mercedes Lackey's Tarma and Kethry) and The Goddess and the Weaver by Spiral Dance.

Avalon:
https://www.youtube.com/watch?v=5BYlEpXQ1gM&list=PLT9lZaywI5eu7AQhhKqHFn41OSR8mBISx

One of Us:
https://www.youtube.com/watch?v=sFZGATwiGeM

Joan:
https://www.youtube.com/watch?v=EfOeANDsXbA

Threes:
https://www.youtube.com/watch?v=0KOUULJuyDk

The Goddess and the Weaver:
https://www.youtube.com/watch?v=SovJQkAHTv0