I'd have to say...
Aphex Twin - Selected Ambient Works 85-92
Bohren Und Der Club of Gore - Black Earth
Miracle Legion - Drenched
Beck - Odelay
Pink Floyd - DSoTM
Boards of Canada - Music Has the Right to Children
I saw them perform a song on the Relapse Concert DVD, and I was really impressed. Even judging by that one song they seem like one of the best bands on that label.