I recommend Garmarna's Hildegard von Bingen album--the arrangements aren't traditional (they're kind of a folk rock group, although the von Bingen album is their least rock-y), but lovely, and Emma Härdelin has one of the most beautiful voices ever.

If you go to "Music" and scroll down, you can download 4 of the songs from that album:

http://www.garmarna.se/

(I'd check out the other albums, too--they're amazing in general.)