I've always been a bit of a fan of Fleetwood Mac, but I only recently found out that the witch that is Stevie de la Nicks wrote an awful lot of their material. Better still, I (astoundingly) only recently heard her song, 'Sara' - do you know it? If you don't, get it on the playlist! It's just quite beautiful, ethereal and, well, you get the idea. I'd love to know what anyone thinks of this. I think it's one of the loveliest ballads I've ever heard, and I know quite a few too!
Other than that, you could try (if you don't already have) any of the following -
Live To Tell - Madonna (very underrated, one of her better efforts)
Angie - Stones
My Foolish Heart - Al Jarreau
I Wanna Be Adored - Stone Roses
Hearts And Bones - Paul Simon
My Cherie Amour - Renee Flemming (covering SW)
I'd agree with the Sarah McLachlan too, quite a few of hers are stunning. Good luck.