YouTube - CLUBROOT - ORBITING
Clubroot is an amazingly talented producer in 2-step, Ambient and Experimental genre. He has two albums packed full with gems which you could easily fall asleep to.
YouTube - Burial - Archangel
"Archangel" is Burial at the height of his powers. A Dubstep and abstract artist who has two critically acclaimed albums to his name already.
YouTube - Aphex Twin - Xtal
Aphex Twin needs no introduction. One of the defining electronic figures for years. Some of his ambient work is unbelievably stunning and chilling whilst creating very intense and sometimes creepy atmospheres at the same time. Unique and ultimately timeless.
Apologies if my links are more Dubstep and not what you were looking for in this thread. However, they are deserving of being referred to as Ambient.