I have always loved a little known Genesis tune called "Silent Sorrow in Empty Boats". The last song on the end of side three(vinyl), it's a 3 minute instrumental that is more ambient than old prog rock.
I remember a thread at the Hypnos forum, a long time ago, that was list of the best ambient tracks by non-ambient artists. I can't find the list or the thread, but I think I added artists like Radiohead, Daryl Hall, Peter Gabriel, etc. I think "Silent Sorrow" may be the best ambient track by a non-ambient artist.
I'm working on a mellow prog rock mix that I'm sure will include this Genesis tune as well.
Anyway, I've always wanted to use it in a mix so here it is. I used the track as the title for this mix but the music doesn't necessarily take on the sorrowful feel that the title suggests. I can personally attest to the fact that this mix works very for sleeping. Enjoy.