Dick Hyman plats Fats Weller on Reference Recordings is excellent. Fred Hersch Songs without Words is solo piano. Most of his other work is with a trio. Art Tatum has a number of piano solo works, though the recording quality on many of these is marginal. All of the Marcus Roberts albums I own are with an orchestra or jazz group. If he has any solo work it would be fantastic. I highly recommend him in concert if you get the chance as well.
Piano only...
I'm looking for albums with only jazz piano only except Keith Jarrett that I already have.