I am one of those people that has to have music on when I go to bed. There's all manner of stuff that I'll go to sleep to - Corrine Bailey-Rea's album got played every night for about a month when I split up with Thomas, Chill out albums (The Art of Chill volume 2 and volume 6 are great for relaxing), Radiohead, Elbow (Guy Garvey is *so* soothing), The Orb, Byrn/Eno. I think the key is for minimal beats, a laid back groove at most, and lots of sonorous sounds - strings, brass, heavily filtered synth pads, heavily reverbed voices - which all points at one band in particular:
Sigur Ròs: Svefn - G - Englar
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I'm not sure I've ever listened to the whole of 'Agaetis Byrjun' without falling asleep...