As far as U2 demos...
- Half of Boy exists in rough demo format (Shadows, Another Time, Twilight, Out of Control, Stories for Boys, Day Without Me) - on those collections listed above
- there is a whole disc devoted to "Two Hearts," with 13 different takes of the song
- there is a "War and Unforgettable Fire Demos" collection that I swear is really nothing more than soundchecks from the War and Unforgettable Fire tour (there is one "Untitled Track" from Unforgettable Fire sessions)
- there is another collection called "Unforgettable Fire Sessions" that is again just live takes of songs, mostly instrumental, I'm guessing culled from soundchecks
- there are 7 30-second excerpts from the Joshua Tree sessions (including early versions of "Still Haven't Found," "Race Against Time," "Walk to the Water," and "Rise Up", as well as three more tracks -- one of which is a definite precursor to Achtung Baby)
- some demos emerged from the "Rattle and Hum" sessions thanks to MP3s of the film and its outtakes ("She's a Mystery," "She's Gonna Blow Your House Down," "We Almost Made It This Time," "Prisoner of Love," "Can't Help Falling in Love")
Since "Salome" the band seems to have really cracked down on leaked demos.