Danny Basavich, but he can play fast too. I have seen him play under a 30-second shot clock at Glass City Open, and he ran a six-pack on Corey Deuel.
Dick Lane is about the slowest I have ever experienced watching, but he sure is a sweet guy, so very nice.
Ralph Souquet plays slow, but he is another one who can speed up his pace, if need be.
Nick Varner is definitely a slow, methodical, calculating, determined pool player. He studies every angle before his fires the trigger. Great player, however, and makes incredible shots.
Reid Pierce, though eye candy for the ladies, has a wee tendency to take his time when in competition.
There's a few more who slow it down from time to time, but the thing about these above-referenced champions is they can all speed it up, if they have to.
In fact, I can think of a few players -- ONE IN PARTICULAR -- who play too damn fast and should slow it down, so that maybe they could not make mistakes, giving their opponents an advantage. I won't name any names.
JAM