Keith Jarrett's an inspiration to me. I have most of his solo improvisation recordings. The only one I find kind of weird is Spheres, his organ improv. It's really really REALLY slow in most parts. Very strange. Still kinda interesting.
His piano improvisations are really good, though he can really grind on one idea for a long time occasionally.
I also enjoy his handel recording, it is very beautiful. It inspired me to pick up some sheet music of some of the suites.
The "Book of Ways" album, all clavichord improvisations, is also really good.
I listen to Jarrett and often wonder why there aren't more well known pianists who improvise as robustly and in as many varied idioms. As far as I know he is literally *the only* well-known one. I've been pointed to numerous other jazz pianists upon saying this in the past, but every one I've checked out leaves me cold with the same, wandering and aimless "floaty" modern jazz sound. Jarrett's own music with his trio leaves me cold, as well. It's really only his solo improvisations that I like.
Here's my absolute favorite section of any Jarrett improvisation: