Paul Sorvino is a regular
Roger Clemens used to come in with Andy Pettitte and Jorge Posada (of course, right after their steroid treatment)
Jerry Orbach and Cory Lidle were both excellent players. Orbach always contributed his time whenever there was a charity event and if you got a chance to see him play, you realized he definitely played at least A-speed for a time. I only met him a few brief times but he always appeared overwhelmingly patient and cordial with whomever recognized him.
Lidle, immediately following his trade to the Yankees became a regular at Amsterdam and befriended most of the club. A solid player, probably around B-speed, I met him because he walked up and introduced himself to me. It was obvious he learned how to quickly establish himself in a poolroom so he could get a good game when he was in town (not for money, just a good game). There was nothing "celebrity" about him. He was often seen either playing or hanging out at the rail, having a beer with the regulars. His nights would end getting dragged to a local diner and splitting cabs home. Very nice guy and still missed.