Thanks for this thread. I've discovered some new pianists and rediscovered a few titles I'd forgotten about.
I'd like to add a couple to the list, first being Marc Copland - he's released a slew of trio, quartet, duet and solo titles for various European labels, many of which are nearly impossible to get.
His most recent release was as a member of the John Abercrombie Quartet - 39 Steps on ECM (which is available as a 24/88.2 download).
Second is Denny Zeitlin. He was a favorite of Bill Evans and opened for him many times. I'd start with the Mosaic 3CD box of his mid-'60s studio recordings for Columbia which include a number of unissued tracks from the original sessions.