Well recorded solo piano and solo acoustic guitar?

Solo guitar -

Julian Bream for classical. He is a classic.

Terra Guitarra has 2 new Spanish influenced CDs, Dragonfly and Firelight. They are a duo, but if you like Spanish style, I think you will like them. “Dragonfly” debuted at #4 on the ZMR World Music Radio Charts and was Nominated ZMR Best Instrumental Acoustic Album of the Year.

Check out any of George Winston's albums on the Windham Hill label.

Clive Carroll, Tommy Emmanuel

Tommy E. is definitely not low-keyed. Totally opposite.

Ed Gerhard, Sunnyland, Any CD from him.
Bill Evans, Alone, Alone Again
Joe Pass, Virtuoso 1-4, Songs for Ellen, Unforgettable
Pink Guitar, Songs from Henry Mancini done on solo guitar.
Laurence Juber, Best
Joe Diorio, Italy
Gene Bertincini, Jobim
Earl Klugh, solo,