I also like singing that kind of music. I've been doing some of the melodies of the "Red book of Montserrat" (I am not very advanced in singing). I especially like "Stella Splendens in Monte". By the way, the Red Book of Montserrat (Llibre Vermell de Montserrat) was a collection of popular medieval melodies the monks of the monastery of Montserrat compiled changing the lyrics so that the pilgrims could sing them during their stay at the monastery. I couldn't find a good interpretation in youtube.com, but here's one anyway:
Stella Splendens in Monte
Alexandros