Heather Dale does make good music, but there are a few other bits of Arthurian related music out there.
Loreena McKennit did a song based on Tennyson's poem Lady of Shallot:
For example, if I am doing something, I will listen to David Arkenstone's stuff for background music.
The vast majority of his stuff is instrumental, but it might be to someone else's fancy. Staying Guenevere/Arthurian mythos specific:
Here is Guenevere's Secret:
There is a whole album called Avalon, a Celtic Legend.
From that is the song Guinevere's Tears:
The following is a piece by a harpist named Lisa Lynne. Yes, it is an instrumental of Fields of Gold by Sting. I actually met her back at a Ren Fair 20 years ago when she was basically taking donations, etc. I bought all her albums that day.
To make it Guen related, sometimes I'll put Lisa Lynne on when playing Guenevere again. And at some point I still intend to make a Troubadour Guen with Morgana.