"Cruisin'" (Smokey Robinson)

The song "Cruisin'" has been covered by a slew of artists.  One of the best and truest renditions was by the Howard Hughes of soul, D'Angelo, in 1995.  There also was a dubious, saccharine version by Huey Lewis and Gwyneth Paltrow a few years later in 2000.  But nothing bests the original by Smokey Robinson from his 1979 album Where There's Smoke...
It's the consummate Robinson song: sensuous, romantic lyrics delivered by that unmistakable tenor over an enduring melody.  In fact, that last point is why the track is a perennial favorite of mine.  There's nothing about Robinson's production that particularly screams "1979": no cheesy synths, no drum machines clacking out a disco beat, no wah-wah guitars scratching away.  Instead, he builds a timeless, smoldering groove atop undulating congas and real, live percussion and then brings the extra sweetness with a layer of lush, but tasteful, live strings.
In short: you won't find a better track to set the mood for amour.