I would put Raison D'Etre and Blut Aus Nord's ambientish stuff under 'creepy' though. They're not exactly peaceful. But, if you're looking for darker and creepier ambient:
Arecibo
Atricum Carceri
Black Lung
Coil (not all of their stuff is strictly ambient though)
Desiderii Marginis
Lustmord
Herbst9
Raison D'Etre (their other albums)
Robert Rich
Thomas Köner
Seconded. You might also want to try some 3rd and the Mortal, the last two Burzum releases (highly recommended) and especially the last Ulver album. All excellent works.
If you're going for GYBE! (which is more post-rock than ambient) I also recommend Explosions in the Sky and Mono (from Japan, not the UK triphop band).
air - virgin suicides soundtrack
aphex twin - selected ambient works, vol.2
craig armstrong - the space between us
sigur ros - ()
mercan dede - sufi dreams (hard to find abroad, but you might pick up anything by this guy if you are into sufism even just a little)
mogwai - rock action
john abercrombie - animato
hooverphonic - a new stereophonic sound spectacular
howie b - folk
jan garbarek - i took up the runes
philip glass - dracula =)
vidna obmana - spore