"Hedphelym" (Ambient Works) and "Beetles" (The Richarddjames Album) are probably his most august pieces in my opinion. That ICCT Hedral isn't so bad either (a bit of a letdown).
I'm not sure what IDM "is", but here are a select few bands similar to those mentioned above (which I also enjoy):
µ-Ziq ("Bluff Limbo")
Venetian Snares
Marumari
Arovane (atleast "Atol Scrap" and "Yeer Disper"; some of the other stuff borders on noise)
Alva Noto + Ryuichi Sakamoto ("Insen", "vrioon", Alva Noto solo is very noise)
gas/high skies (em:t0095, which means extreme quality. actually, the whole em:t output, EVER is extreme quality. borders on ambient though.)