Favourite ECM Titles

Nik Bärtsch's Ronin-Holon
Tomasz Stanko Quartet-Suspended Night
Steve Reich-Music for 18 Musicians
Ketil Bjornstad & David Darling-Epigraphs
All of Tord Gustavsen's albums are a must with Being There being my favorite
Keith Jarrett-The Koln Concert
Terje Rypdal-Rarum VII is a good place to start since it has cuts from various points in his career. Great guitar work.
Tons more but those are the first releases that jump out at me.

John Abercrombie, Jan Hammer, Jack De Johnette - Timeless
Gary Burton - The New Quartet
Keith Jarrett - Solo Concerts - Bremen and Lausanne
Steve Reich - Music For 18 Musicians
Chick Corea - Return To Forever

West German vinyl sounded much better than the US releases.

Several choice albums have already been mentioned. I'd like to add:
"Conference Of The Birds" Dave Holland
"Yellow Fields" Eberhard Weber

Molvaer Nils Petter 'Khmer'
Pat Metheny 'Offramp'
Carla Bley 'Night Glo'
Carla Bley 'European Tour 1977' especially 'National Anthem in Minor...'

Pretty deep well... a few favorites:
Gateway (1st)
Eberhard Weber (The Morning After)
Terje Rypdal (Whenever I Seem To Be Far Away)
Contact Trio (Marks)
Gary Burton (Dreams So Real)
Dave Liebman (Lookout Farm)
Old and New Dreams (Playing)
Louis Sclavis Quintet (L'affrontment des pretendants)
Julian Priester (Love Love)

Lots of others deserve mention, but would replace these fast if I had to start over.