There are a lot of good players on here, who do not necessarily stay active on all boards. Some who I've noticed are (in no particular order): hakki, arielpiano, rachfan, furiouzpianist, birba, andhow04, teresa_b . . . I know there are more whose playing I like but cannot think of them all right now. And, of course, I agree with some who have already been mentioned.
Derek and ted have posted some impressive improvisations.