I'm quite suprised to find that most respondents' choices come from one of the other ECM catalogue. I would like to recommend a couple of disc from the ECM New Series catalogue: Officium (ECM 1525) and Mnemosyne (ECM 1700/01). Both by Jan Garbarek and The Hilliard Ensemble. Here in U. K., Officium is without doubt the best selling ever ECM album, although listed as both a Jazz and Classicsl CD. The latter, it was in the top 100 chart since its launch in 1994. Even today, whenever the Classic FM radio station played tracks from these two albums, the radio station's phone line just went ballistic with people ringing in enquiring about what CD they were playing.