These are just a few favorites; some that work for me within the context of the song, while others work for me on their own terms. And contrary to the constitution of atease, I'm gonna actually be sincere! (maybe a little too much so!)
True Love Waits
Perhaps my favorite Radiohead lyric; if not my favorite, the one I think back on the most. I've lived with depression for at least the last six or seven years of my life, and this is a remarkably succinct description of what living with depression feels like to me. Thom correctly delineates between living and merely existing.
"Fitter Happier" prefigures the cut-and-paste lyrical snippets that made up much of the material on Kid A, and I think it's arguably Thom's most successful experiment in that style. Some may find these lyrics juvenile, but I find that they only resonate more as I get older. An endless supply of words have been written about how OK Computer predicted the dystopian side of the Internet age, but really: is there a song that better predicted our increasing infatuation with, and the exponential proliferation of, shallow self-help bullshit? You are now fully optimized.
Simple, innocuous lyric made transcendent in context of the song. It's another one that resonates with my experience with depression. Shortly after becoming a homeowner I parked outside the house one evening and thought of this line. I had "made it" - a house, a career, a wife, kids, etc. So how could I feel so sad? Moreover, what right did I have to feel so sad? I was very fucking fortunate, all things considered. "No Surprises" is wary of a pretty, "optimal" exterior hiding a hollow interior, and it's captured perfectly at this climactic moment.
Motion Picture Soundtrack
Just a brilliant opening stanza, juxtaposing the concrete imagery of solitary pleasures we use to cope - "red wine," "sleeping pills," "cheap sex," "sad films" - with their inability to bring us the kind of human connection we yearn for, let alone get us "where [we] belong." It's devastating, but fucking beautiful.
I love this opening stanza for the same reason @myth does: it captures, through some very sharp imagery, what it feels like to be thrown into a terrifying situation you can't escape from. It seems reasonable to think that this is a direct reference to Rachel's cancer diagnosis, and that's how I've chosen to interpret it. I received a cancer scare myself last year - I was showing all of the symptoms of a certain kind of cancer - and in the weeks leading up to my operation to verify if I did or not I kept coming back to this song. You want to put your head in the sand, to make it all go away by pretending it's not there, but the thing is so huge - a "spacecraft blocking out the sky," "the loudest sound you've ever heard" - there is no escape.