"Ain't No Sunshine" (Bill Withers)

I can't express my respect and admiration for Bill Withers enough.  If you want to know why I'm such a fan, just watch the documentary Still Bill (2009).  You'll see a portrait of an intelligent, humble man who also happens to be one of the best songwriters of the 70s.  He's also highly principled: instead of kowtowing to trends and giving in to record execs who kept telling him how they thought his music should sound, he simply walked away from the industry in 1985 and went to raise a family instead.  (In the film, he tells a story about a white A&R guy who tried to convince him that a cover of Elvis's "In The Ghetto" was going to be his ticket to a pop hit.)
My favorite track of his (largely because it's the first one I ever heard) still is "Ain't No Sunshine" from his debut album, Just As I Am (1971).  It's a deceptively simple song: a short phrase ("I know") that gets repeated a total of 26 times, bookended by a few short lines that (on the surface) are about longing for lost love.  
As a little kid, I liked the track because it was easy to learn and remember.  I also enjoyed the counting game that my mom would play with me, where she'd challenge me to count the 26 I know's.
But as I got older, I started to realize that "Ain't No Sunshine" isn't some torch song, where ol' Bill is pining away for his woman.  It's a song about the vicious cycle of dependency.
Withers pretty much confirmed this in a 2004 interview with Carl Wiser of Songfacts.com.
"It's pretty obvious what it's about.  I was watching a movie called Days Of Wine And Roses (1962) with Lee Remick and Jack Lemmon.  They were both alcoholics who were alternately weak and strong.  It's like going back for seconds on rat poison.  Sometimes you miss things that weren't particularly good for you.  It's just something that crossed my mind from watching that movie, and probably something else that happened in my life that I'm not aware of."
Musically, it's beautifully melancholy.  But it also grooves like crazy.  After all, he had 3/4 of Booker T. & The M.G.'s (minus Steve Cropper) + Stephen Stills backing him on the single.

"Carry On/Questions" (Crosby, Stills, Nash & Young)

I'm not just a fan of CSN (and sometimes Y); I'm a fan of Stephen Stills, specifically.  He's one of the few rock musicians I know of who could tackle everything from acoustic folk to blues-drenched R&B and actually make it sound natural.
Case in point: his mini-suite "Carry On/Questions" from the album Déjà vu (1970).  It begins with this galloping acoustic portion that feels almost like an Indian raga before seamlessly transitioning into this funky Hammond organ-driven groove.  It's two things that probably shouldn't work together, but they do.
The track consists of two songs that Stills had been working on but never quite finished.  They needed an opening track for Déjà vu, and bandmate Graham Nash suggested they open with a suite in the same vein as "Suite: Judy Blue Eyes" from their debut.  So Stills took his incomplete composition "Carry On," which is basically a message to his bandmates to persevere, and melded it with "Questions," another incomplete composition that had been knocking around since his days in Buffalo Springfield. 
What makes the track hold together (apart from the note-perfect instrumental backing, which features Stills on both acoustic and lead guitars as well as organ, bass, and percussion), is that three-part vocal blend.  My favorite part is the a cappella transition, where they intone Love is coming / Love is coming to us all.  Gives me chills every time.

"You Don't Have to Cry" (Crosby, Stills & Nash)

Having an eidetic memory is a double-edged sword.  On the one hand, I have this storehouse of vivid memories of even the most mundane moments with loved ones.  On the other hand, every embarrassing and painful incident from youth can be referenced just as easily.
So what does that have to do with "You Don't Have to Cry" by Crosby, Stills & Nash?
When I was 3, our next door neighbors moved away.  They were the only people with kids my age in our rural neighborhood, and their departure upset me quite a bit.  (Especially when it finally sank in that they were moving to Iowa—a state that was almost 1,000 miles away, and not Etowah—a town that was just five minutes away.)
Before they left, they had a massive yard sale, and I went with my dad to do the neighborly thing: say our goodbyes and buy a few things.  We ended up with a couple of hand tools and a copy of Crosby, Stills & Nash's 1969 debut album.  When we got home, Dad put the album on the stereo.  We sat, lounging on the sofa—"cooling it" (as Dad liked to say), listening to those indelible three-part CSN harmonies.  For some reason, it suddenly hit me that I probably wouldn't see Chrissy and Dylan again, and I started to bawl.  Dad kept asking what was wrong, and I tried to express what was going through my little kid brain, but all that came out was something like: "BUH-BUH-sniffle-sniffle-UGH-UGH-sniffle-sniffle."
Call it serendipity or coincidence, but the album hit track #4, "You Don't Have to Cry," at that very moment.  And when I heard the chorus (Cry, my baby / You don't have to cry / I said, cry, my baby / You don't have to cry), it was like a personal message: I didn't have to worry, I didn't have to be sad, and my pals would be fine in Iowa (wherever the heck that was).  I calmed right down.
Ever since, it has been a song I turn to when I need a little reminder that things could always be worse.
But that's not really what the song is about.  Stephen Stills wrote it about his ex-girlfriend, folk singer Judy Collins, addressing the fact that she chose the trappings (and traps) of fame over their relationship, leaving him heartbroken.  (The track "Suite: Judy Blue Eyes" also is a chronicle of their doomed relationship.)
Incidentally, "You Don't Have to Cry" also was the first song the trio ever performed together.  Stills (who'd recently left Buffalo Springfield) and Crosby (who'd just been kicked out of The Byrds) met in 1968 at a party at Mama Cass Elliot's house in the Hollywood Hills.  Story goes, when Elliot heard the two harmonizing, she immediately knew her buddy Graham Nash, who was looking to leave The Hollies, would be the perfect third voice to round out the vocals.  So she arranged for Nash to meet Crosby and Stills at her place.  They played through "You Don't Have to Cry" twice as Nash sat and listened.  The third time through, Nash added his high harmony, and they immediately knew they had a group.

"For What It's Worth" (Buffalo Springfield)

It's almost ridiculously simple: an understated acoustic guitar playing a single chord, paired with an electric guitar with the tremolo cranked up, playing the same two-note pattern, over and over—plucking the 1, plucking the 5, and then back down to the 1 of the scale.  It doesn't sound like a formula for any kind of hit song.  But that's the structure of "For What It's Worth" by short-lived folk-rock band Buffalo Springfield.
The song was penned and sung by Stephen Stills, who most notably went on to form supergroup Crosby, Stills & Nash after Buffalo Springfield imploded (the result of creative tensions between Stills and bandmate Neil Young and various members getting busted—and even deported—for possession).  Although it's often assumed that the track is a protest song about the Vietnam War, that's not the case.  Stills wrote it after witnessing a run-in between police and students on LA's Sunset Strip.
There were a number of bars and clubs geared to teens and college students along Sunset Blvd.  Various business owners and older residents had grown tired of kids congregating outside the late night clubs, and they pushed to have a "no loitering" ordinance passed, which stipulated a 10 pm curfew.  Students saw this as a violation of their rights, so they took to the street outside a club called Pandora's Box (currently the site of a traffic island, across from a strip mall).  Things started peaceably enough.  But as the number of student protestors grew and they started blocking traffic, that's when the riot squad got called in.  Stills wasn't directly involved in the protest; he'd merely driven through the area, saw the tense situation, and turned right around and headed home, where he came up with the music and lyrics in a matter of minutes.
A close read of the lyrics reveals that it's neither explicitly pro-students nor pro-police; it's merely a chronicle of the event by a bystander who can't really comprehend how things got so out of hand.  In short, you have the students marching and holding picket signs on one side because they're pissed off about a curfew, and then police overreacting on the other.  That's why the refrain (I think it's time we stop. Children, what's that sound? Everybody look what's going down) is just as important as the line Nobody's right if everybody's wrong, in my humble opinion.
So it's not a protest song.  But it is one hell of a piece of journalism, set to the funkiest backbeat in all of 60s folk-rock.