Ultraviolet (Light My Way)
Edit:
Numb (Zooropa)
Stay (Zooropa)
Sunday Bloody Sunday (War)
Pride (In the Name of Love) (The Unforgettable Fire)
One (Achtung Baby)
Who's Gonna Ride Your Wild Horses (Achtung Baby)
Mysterious Ways (Achtung Baby)
Tryin' to Throw Your Arms Around the World (Achtung Baby)
Ultra Violet (Light My Way) (Achtung Baby)
Love is Blindness (Achtung Baby)
Where the Streets Have No Name (Joshua Tree)
I Still Haven't Found What I'm Looking For (Joshua Tree)
With or Without You (Joshua Tree)
Running to Stand Still (Joshua Tree)
Red Hill Mining Town (Joshua Tree)
Mothers of the Disappeared (Joshua Tree)
Beautiful Day (ATYCLB)
Stuck In A Moment You Can't Get Out Of (ATYCLB)
Walk On (ATYCLB)
The "ultimate" U2 album would also include live renditions of all of these.
I am sure there more great U2 songs from their Boy, War, October, and The Unforgettable Fire albums, but I am not as familiar with them.