I'm not sure to what extent these constitute dark ambient (the distinction gets a little blurry for me), but I've heard them mentioned in the same realm as dark ambient, so I would also recommend Maeror Tri (The Beauty of Sadness), Dargaard, Zoviet France, Dark Muse, and Rainforest Spiritual Enslavement. Some of Nadja's and Prurient's stuff edges into that territory as well (though the former is mostly drone/doom).