Tangerine Dream - Phaedra, Zeit, Alpha Centauri
Loscil - Plume
Aphex Twin - Selected Ambient Works Vol. 2
M. J. Harris & Martyn Bates - Murder Ballads
Mirror - I paint for the love of color, Nightwalkers, A Pilgrim's Solace... Any of them pretty really I love Mirror
Andrew Chalk - Time of Hayfield, same goes here, Chalk is half of Mirror)
Thomas Köner - Nuuk
Michael Bross - Subway Meditations
Akira Yamaoka - Silent Hill 1, 2 and 3: The Complete Soundtracks to all three
Jorge Reyes - Mort Aux Vaches, The Flayed God and if that's up your alley be sure to check out Antonio Zepeda as well!
William Basinski - Melancholia, The Disintegration Loops
Oöphoi - The Rustling of Leaves, The Spirals of Time and so many others

And some borderline ambient, but might scratch the itch:

Gavin Bryars - Jesus blood never failed me yet
Jon Hassell - Vernal Equinox, The Surgeon of the Nightsky Restores Dead Things by the Power of Sound, others from his earlier half
Rapoon - Vernal Crossing
Tuu - All Our Ancestors
The Body Lovers/The Body Haters
Scott Walker - The Drift, Tilt
Dead Can Dance - The Serpent's Egg, Into the Labyrinth, Toward the Within, Within the Realm of a Dying Sun

edit: There's too many! I didn't get to Robert Rich, Gas, Jan Jelinek, Muslimgauze, Biosphere and so many others