I've noticed that the last song on a handful of Porcupine Tree albums have an interesting effect on me. They are often very slow and bleak, and when I first heard the albums, I usually would skip past the last song. But over time I warm up to those tracks and they become some of the most interesting, moving, profound songs.

top ones:
1) Collapse the Light into Earth (though I like the version on "Futile" a bit better, and there it's the opening song)
2) I Drive the Hearse
3) Feel So Low

I'm not the biggest fan of Sleep Together or Glass Arm Shattering. Though actually my copy of Deadwing ends with a 2004 version of Shesmovedon, which I would list as #4. Chloroform, which ends "Futile," is pretty good too, but lyrically it seems to stand a bit outside of the other songs.