Boy: Out of Control
October: Tomorrow
War: New Years Day
The Unforgettable Fire: The Unforgettable Fire, and that has NOTHING to do with favoritism, you could easily have A Sort of Homecoming here as well. As far as the sound of the albums' concerned it doesn't get more obvious than that.
The Joshua Tree: This is harder, because if I'm looking for the sum of the SOUND of the album, that's hard, because the album's a bit all over the place, but Streets is probably the way to go, because, yeah that's what I most associate with the album.
Rattle & Hum: Weird, but I associate All I Want Is You the most with this album, but to actually sum up the SOUND of the album, I'd actually go with Helter Skelter
Achtung Baby: The Fly, and I don't even LOVE that song or anything.
Zooropa: This is hard in the same way that TJT is, there isn't a clear sound on here. I associate this album most with the title track, I suppose, just because.
Pop: Gone for whatever reason, that's more a gut feeling.
All That You Can't Leave Behind: Beautiful Day. Every time.
How to Dismantle An Atomic Bomb: I associate this one the most with Vertigo, but I get the most out of City of Blinding Lights, for whatever that's worth
No Line on the Horizon: Breathe or Moment of Surrender, both fit the different moods of the album best in their own ways.
This post started out pretty well, but then I got really confused with my own feelings about halfway through and almost ditched the list, but then, I just figured, wtf, in the end it's just a list on the interwebz, make of it what you will.