My favorite thing about Radiohead is that most of their songs build up to a climactic moment. And if you were to start playing the song at that climactic moment, it would seems like complete chaos. In "Fake Plastic Trees", it's when the drumming comes in, right before the line "She looks like the real thing, she tastes like the real thing...", which is why I think I love the line so much.
As for In Rainbows, "15 Step" has to be one of my top five, if not three, Radiohead songs.