How about the beautiful and Gregorian-sounding "Deus Meus" ? I don't have any references on it to hand (and no time to search for any right now) but it's well worth consideration. The Irish group Na Fili recorded it some years ago (I think the album was called "A Kindly Welcome" but I could be mistaken). Anyone add any further info to this? Unfortunately I'm rushing or I'd find it myself -