At late night, when I listen to jazz, I most often listen to piano, either solo or with one other instrument. In addition to some of the albums listed in previous responses, here are long-time favorites and some that I've been enjoying recently:
Ahmad Jamal -- Ballades
Fred Hersch -- Music from Home
Bill Evans -- Sunday at the Village Vanguard and Waltz for Debby
Charlie Haden and Hank Jones -- Steal Away and Come Sunday
Charlie Haden and Chet Baker -- Silence
And some exceptions to the rule include:
Ben Webster -- Soulville (yep, I'll join the chorus on this one)
Ben Webster -- Jazz 'Round Midnight
Pat Metheny and Brad Mehldau -- Across the Wide Missouri Sky
Joe Pass -- Meditation and Unforgettable
Happy listening and sweet dreams!
Jim