"Come As You Are" (Nirvana)

Even now, when I hear Kurt Cobain's burbling, underwater riff that opens "Come As You Are," it stirs something within me.  (Forget the fact that he subconsciously lifted it from post-punk band Killing Joke.  Besides, there were no hard feelings in the end.)  That intro reminds me of the simultaneous relief and exhilaration I felt as a teenager when there was a worthy successor to "Smells Like Teen Spirit."  It signaled that Nirvana wasn't some flash in the pan, and the over-produced schlock that had passed for rock for half a decade was finally dead.  
I just wish Cobain would have hung around a bit longer to embrace and enjoy what he'd helped create.
Over the past few days as I was poking around the internet, brushing up on the facts of "Come As You Are," it became clear that the song (like many others that Cobain wrote) is a mosaic of personal experiences—not blatantly autobiographical, but still intensely intimate.
The most enlightening thing I stumbled across was an article from early 2014 about the possible origin of the song's title.  When Cobain was in his teens, his father kicked him out of the house for bad behavior.  For a brief time, he stayed with his alcoholic mother but then took off when the two had a falling out, which rendered him effectively homeless.  Apart from occasionally crashing with friends, he spent most of his nights seeking shelter in old/abandoned buildings around his hometown of Aberdeen, WA.  According to biographer Charles R. Cross, Cobain also occasionally crashed at a flophouse in Aberdeen called The Morck Hotel, which advertised using the slogan: "Come as you are."  (By the looks of the Morck's website, it's currently going through a major renovation to become some kind of upscale boutique hotel.  Figures.)  
When I think about the lyrics of the song (which involve people contradicting themselves by saying one thing but really meaning/expecting another) in the context of Cobain's experience as a teenager, the pieces begin to fall into place.  His experience also sheds light on the use of the word memoria, which gets repeated throughout the song.  Memoria is one of the elements of the art of rhetoric.  Basically, it means recalling a bit of knowledge or experience to support your argument.  (The fact that he puts the emphasis on the wrong syllable, making the word rhyme with "diarrhea," also isn't an accident, in my opinion.)
In short, he's questioning whether you can take people's rhetoric at face value.  (Would you be inclined to believe someone who claims they don't have a gun?)
Along with that, it's about actions speaking louder than words.  Or as the late Maya Angelou put it: "I've learned that people will forget what you said, people will forget what you did, but people will never forget how you made them feel."

"Smells Like Teen Spirit" (Nirvana)

I kind of feel bad for including "Smells Like Teen Spirit" from Nevermind (1991) in my list, considering how tortured Kurt Cobain was by the song at the end of his short life.  (As he once told Rolling Stone, "On a bad night, I can barely get through 'Teen Spirit.'  I literally want to throw my guitar down and walk away.  I can't pretend to have a good time playing it.")
But the song still means a lot to me.  And I'm not just saying that to jump on some generational bandwagon.  The moment I heard/saw the video for it on MTV, I felt like I was witnessing history: this was the antidote to all of the overblown rock and pop that had been shoved down our throats during the latter part of the 80s.  It was raw and intense in a way that revealed all of the bands riding the top of the Billboard charts in those days for the crap peddlers they really were.
But the most striking thing to me was that Cobain & Co. weren't merely telegraphing some tired sentiment like "it's cool to be uncool."  This song/band didn't give a shit about being cool.  "Cool" was some concept that advertisers had invented to make you feel bad about yourself so you buy stuff you don't need.  
No, this was a generational call to arms to stop being apathetic and stop blindly consuming bullshit.  And it rocked.
As soon as the video ended, I imagined everyone from MC Hammer to Axl Rose screaming at their agents on the phone, "What the f*** am I supposed to do after that?"
Quick side note about the song's origins: in 1990, Cobain was hanging out in Olympia, WA, with his friend Kathleen Hanna from the punk band Bikini Kill.  (She recounts the story in this great video from 2010, when she performed a cabaret act of sorts at Joe's Pub in NYC.)  In short, they got stinking drunk and wound up back at his apartment, where Hanna proceeded to write a bunch of stuff on his bedroom wall in Sharpie pen, including the taunt "Kurt smells like Teen Spirit."  (Apparently, her bandmate Tobi Vail, who was dating Cobain at the time, wore Teen Spirit deodorant.)  Six months later, Hanna got a call from Cobain, asking her permission to use the bit of graffiti for a song he was working on.
Said Hanna, "I hung up and I was like, how the f*** is he going to use 'Kurt smells like Teen Spirit' as a lyric?"

"Lithium" (Nirvana)

I loved the song "Lithium" from the moment I heard it.  Its shifting dynamics.  The almost-jazz feel of the verses set against the crunch of every chorus.  Kurt Cobain's ardent cries of I'm not gonna crack.  It was just the perfectly crafted rock song that didn't feel crafted at all.
As the third, formidable single in a row released from Nevermind (1991), I think it signaled to the world that Cobain wasn't just some lucky bastard who'd scored a major label recording contract.  He had intelligence and a real talent for writing damn good songs.
"Lithium" was mostly inspired by Cobain's stint, staying with his friend Jesse Reed's born-again family when he was a teenager.  Cobain's dad had kicked him out of the house for bad behavior, and the Reed family took him in.  During his stay, he became a frequent churchgoer but became disillusioned in time with religion.
In the song, the protagonist has lost his girlfriend (apparently, she's died), and he's struggling to find the will to stay alive himself.  So he turns to religion to save himself—the metaphor being that religion is a drug, like lithium, that serves to numb the pain of life and gets you through another day.
Although the story in the song is itself fictitious, in real life, Cobain pretty much felt that, if religion worked to keep someone sane/happy/alive, then rock on.