I do rather rate RA MacAvoy's long ago trilogy, starring Raphael and set in the Renaissance. Not exactly a romance though. Long out of print sadly, MacAvoy has never really had the success she deserved. Took ages for me to track the last one down on Charing X Road
Ooh, actually looks as though the ebook revolution may do something for her: Damiano; Damiano's Lute; Raphael