Sarah Mclachlan: The freedom sessions or fumbling towards ecstasy
Norah Jones: Not too late or Come away with me
Joni Mitchell: Blue or Court and Spark
Gillian Welch: Time the revelator and Revival
K.D. Lang: Ingenue or Shadowland
Rickie Lee Jones: Rickie Lee Jones or Pirates
Bonnie Rait: luck of the draw or nick of time
Natalie Merchant: Ophelia
Anne Sofie Von Otter: Marian Cantatas and Arias (Handel) (first heard this in an Avantgarde demo at CES, great music and recording)
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while I'm at it:
Miles Davis: kind of blue (make a lot) some day my prince will come
John Coltrane: many, but e.g. a love supreme
Willy Nelson: stardust (a classic)
Lyle Lovett: live in texas and step in this house
Neil Young: greatest hits, comes a time, ... many
Knopfler/Harris: all the roadrunning
Tom Waits: Nightwawks at the diner and heart of saturday night
James Taylor: greatest hits + many
All of these are recorded well enough to be demo material, but they are musically great as well!