After Daniel Lanois, Michael Brook naturally comes to mind. He's another guitarist whose strength is in colors and atmospheres rather than power and speed. And Lanois produced Brook's album Cobalt Blue, which is well known among both guitar and ambient music fans--I first heard it on the ambient radio program Music from the Hearts of Space. He invented something he calls "infinite guitar", which I take to mean that it can sustain a note until the player decides to stop it.
"Ultramarine" (apparently this was used in a movie called Heat):
If you like these, you won't be disappointed in the album. And if you think you hear a suggestion of Joshua Tree-period U2, especially in "Ultramarine," it's apparently not a coincidence.