Hmmm. I'm thinking this is an awful subjective kind of thing, but maybe something from Leonard Cohen, like, Take this Waltz, A Thousand Kisses Deep, Dance Me to the End of Love, or Alexandra Leaving, the one done as a duet with Sharon Robinson.
Or, He Wants You, from Nick Cave & the Bad Seeds
Also, they're old (lol, not that those others are not), but I like Springsteen's original Secret Garden (NOT JERRY MCGUIRE REMIX THING!) and Billy Joel's cover of Cohen's Light as a Breeze.
Wonderwall, maybe, from Ryan Adams. In the Backseat, from Arcade Fire?
Gah, this is something one could go on forever with, really, considering.
Not to mention any of a number of so many violin concertos, goodness.
I dunno - but good luck, and have fun with all of that!