oh, man he has so much good impro/experimental stuff. from the top of my head from those official releases :
Drift, Vancouver Ambients 1-4, North Six, Broken Circle, From Here To Infinity, SCRIPTURES OF THE GOLDEN ETERNITY, Amarilo Ramp, Dirty Windows, Music For Stage And Screen, Oasis Of Whispers, Celestial Answer, Nothing Makes Any Sense, Outside My Window...
And I am really enjoying using his spoken word into my mixes. Especially Spoken For Geraldine, which I have on tape and
he has tons of experimental stuff there and it is never disappointing.