This is an old thread, but I'm gonna post this anyway.
Boy: Another Time Another Place - Probably one of the better songs from Boy, yet it seems to be one of the least known. I've always found it catchy.
October: Tomorrow - Such a great song. October is pretty underrated, and so is this song. One of the better early U2 songs.
War: The Refugee - This song is one of the least talked about from War, and it seems to be the most disliked for whatever reason. I always thought it was kickass.
The Unforgettable Fire: Bad - This may seem like an odd choice, but among non-U2 fans, this song isn't really known (compared to WoWY, ISHFWILF, One, etc). This one of the songs that shows how incredible Bono can sing and I'm surprised it isn't one of their most well-known songs.
The Joshua Tree: Red Hill Mining Town - I almost picked Mothers of the Disappeared, but I decided to go with this for a couple of reasons. Before the Joshua Tree 2017 tour happens, this song has never been performed live. It was supposed to be the first single originally, and ended up not as one at all due to various reasons such as it being hard on Bono's voice and the music video that was shot not being good. It seems to be very well-liked by U2 fans, but like Bad, this should be on their premier songs that everyone knows, and it is not.
Rattle and Hum: Heartland - Possibly my favorite song from Rattle and Hum. I listened to U2 throughout my childhood and I didn't know it existed until I rediscovered them. Very underrated.
Achtung Baby: Tryin' to Throw Your Arms Around the World/Ultra Violet (Light My Way) - Achtung Baby is full of great songs, and for some reason this one always seem to be forgotten. I would actually rank it in my top three from the album. I love listening to it. EDIT: I have added Ultra Violet as well due to my intense love for that song. This is another that should be considered a U2 classic, but doesn't seem to be known by anyone who isn't a U2 fan.
Zooropa: Daddy's Gonna Pay for Your Crashed Car and Stay (Faraway, So Close!) - I tried desperately to only choose one song for each album, but I just couldn't here. Daddy is unknown by casual U2 fans and a decent amount of hardcore U2 fans don't care for it. This one of the songs that reignited my interest in U2 after I rediscovered them. It's just awesome sounding. Now, Stay is well-liked by Bono himself and a lot of U2 fans, but it is not nearly as popular as it should be. It's another one of those songs that really show off his voice, and it's one of most "normal" songs from Zooropa. It should have been a hit.
Pop: The Playboy Mansion - Not my favorite from the album, but a very good and underrated song. This whole album is underrated, but this is the one song that seems to be forgotten by everyone. I don't believe it was ever performed live either. (I think the band couldn't perform it to their liking or something like that).
All That You Can't Leave Behind: New York - I had a hard time deciding between When I Look At The World or this. Both are great. I've always really liked the guitar that loudly kicks in during this song. I also love the atmosphere. It deserves more attention.
How to Dismantle an Atomic Bomb: Love and Peace or Else - Such an awesome song. Vertigo is good, but this is much better. This should have been the lead single if you ask me. This album gets too much hate, and this is one of the quality songs I point to when I hear people talk shit about it.
No Line on the Horizon: Get on Your Boots - One of the most hated U2 songs, and why? Is it incredible? No, but it is a cool song. Some people don't care for it, and that is fine, but some people HATE it and I have no idea why. I have always liked it.
Songs of Innocence: This Is Where You Can Reach Me Now - It seems to be the least known song from the album, which I find odd. I didn't like this album originally, but this was one of the first songs on the album to grow on me. It's still one of my favorites from the album (which as a whole I know like a lot).
So that's my list. There are MANY more songs which I believe are underrated, but that is my attempt at doing about one for each album.
EDIT: Holy crap I wrote a lot! I'm gonna put each song in bold to help those who don't want to read all of that...
