On this thread, I've noticed One Tree Hill mentioned as if it hasn't been released as a single. To my knowledge, that is false: it was actually released in a single in Australia and New Zealand (don't know if it was a completely separate release or replaced In God's Country, but I'm positive it was released as a single over here).
Now, to answer the original question of this thread;
- Bad (This really should've been released. I have no idea why it wasn't)
- A Sort Of Homecoming
- Seconds
It was too hard to choose, really. Stuff like Tomorrow, The Three Sunrises, The Electric Co. (UABRS), Gone, and all that really should've been released. I once did a chart of the 148 U2 songs I either have on CD or on my hard drive (and I was going to omit those from videos but loved 3 so much I had to add them), and all the songs down to about 133 I thought should've been released as singles (if they hadn't been already). To me, it's irrelevant if they would've been big hits or not - they're marvellous songs and should've been released. The general public seems to have crap tastes so if it charted or not, it wouldn't bother me too much.