"You're All I Need to Get By" (Marvin Gaye & Tammi Terrell)

"You're All I Need to Get By" (1968) is one of the best ballads ever released by Motown.  The Nick Ashford and Valerie Simpson-penned track is dramatic without drifting into the realm of melodrama.  It works because, even with those dulcet strings, you have The Funk Brothers rhythm section keeping the song rooted in soul along with Marvin Gaye and Tammi Terrell delivering their vocals with gospel-tinged fervor.  It's passionate, and it's honest.
As I've written before, Terrell and Gaye weren't actually romantically involved.  Although, that's almost hard to believe, listening to a performance like "You're All I Need to Get By."  I think it's fair to say that they were soulmates.
While performing with Gaye at Hampton-Sydney College in Virginia, Terrell, who had been prone to migraine headaches her entire life, collapsed on stage in Gaye's arms after complaining that she wasn't feeling well.  Turned out that she had a malignant tumor, growing in her thalamus.
Recovering from the first of many operations and wheelchair-bound, Terrell still wanted to record, and "You're All I Need to Get By" was the first single that she worked on, post-surgery.  Because of their schedules (and also to allow Terrell sufficient time to rest and recover), she and Gaye didn't cut their vocals together in the studio; their vocals were recorded separately and then edited together as a duet afterward.  Nevertheless, there's still a palpable feeling of unity on the track.  And under the difficult circumstances, I think it's even more poignant that they were singing to each other (even if it was via studio wizardry): you're all I need to get by.

"Your Precious Love" (Marvin Gaye & Tammi Terrell)

"Your Precious Love," penned by famed songwriting team Nickolas Ashford and Valerie Simpson, is simply one of the sweetest, sultriest love songs ever recorded.  It was made for pulling someone in real close and swaying in time till the rest of the world fades away.
Everything about this track works: the finger clicks, Joe Messina's lead guitar doubling James Jamerson's slick bassline, the smooth doo-wop style backing vocals, and—obviously—Marvin Gaye and Tammi Terrell's perfectly blended vocals.
Even though Gaye and Terrell weren't romantically involved, you kind of wouldn't know it, listening to this song.  They sound like two people who are deeply in love.
Which is pretty heartbreaking if you know anything about Terrell's life.  
Born Thomasina "Tommie" Montgomery in Philadelphia in 1945, she weathered a difficult childhood.  On top of dealing with her mother's bouts of clinical depression and fallout from shock therapy treatments, she herself suffered from debilitating headaches, which foreshadowed her death at the young age of 29 from a malignant brain tumor.
She also was raped by several neighborhood boys as a pre-teen.  As the TV One documentary Unsung: Tammi Terrell notes, in the wake of the incident, she decided she no longer wanted to be called Tommie and changed her name to Tammi.  She even recorded a few songs under the name "Tammi Montgomery" before landing a contract with Motown.
Sadly, the traumatic event set the tone for her rocky relationships with men for the rest of her life.  
In her late teens, she toured with and also dated James Brown for a time.  Until he hit her.  Repeatedly.
Then, after she signed to Motown Records (where founder Berry Gordy changed her name to "Tammi Terrell," simply because he thought it looked better than "Tammi Montgomery" on the label of a 45 single), she fell for the already-married David Ruffin of The Temptations.  Unfortunately, Ruffin also physically abused her.  Although, this time around, she hit back.
In truth, Gaye was one of the only men in her life who treated her with respect.
And when you hear the emotion come through in her voice on "Your Precious Love," it's clear that the relationship she's singing about is exactly the kind of unconditional, transcendent love that she desired.