Bill Evans fans, check out the Oscar Peterson Trio, Red Garland Trio, and McCoy Tyner Trio. Garland played piano for Miles, and Tyner played for the great one - Coltrane.
"Mingus Plays Piano" is also a lovely solo piano album. Get the 20-bit remaster on CD, the HDTracks release isn't nearly as good.
Some of my other favorite mellow albums:
Blue States - Nothing Changes Under The Sun
Brian Eno - Apollo, Discreet Music, Music For Airports (ambient genesis), Neroli, The Pearl, Thursday Afternoon
Ishq - Orchid, Sama, Fluid Earth, Lotus
Solar Fields - Leaving Home, Earthshine, Movements, Origin, Altered
Steve Roach - too many albums to list
Ulrich Schnauss - A Strangely Isolated Place, Far Away Trains Passing By, Goodbye
William Orbit - My Oracle Lives Uptown, Hello Waveforms, Strange Cargo IV:Hinterland
Carbon Based Lifeforms - World Of Sleepers, Hydroponic Garden, Interloper