Agree with many already mentioned, I'll add John Greaves of Henry Cow and various other Canterbury related bands. He can play solid grooves, float time when necessary is a great improvisor and has a real handle on odd time signatures.
New to this thread. I'd been re-listening to some old Henry Cow and had to search TB to see if he gets any props up here. John Greaves is an amazing player, and just as proficient on piano. Real Monster.