Archie Moore and Ezzard Charles (at least at heavyweight, I think he was quite mobile as well at light heavy) are two of the most obvious choices here, guys who could stand right in front of you and make everything you threw glance off ineffectually with well-timed upper-body shifts, shoulder rolls and the like. They were idols of the man who, of course, is the modern exemplar of the style being discussed; James Toney.
I've just tho0ught of another one, a great one, Jose Napoles. Not super fast, but certainy very very slick. An aggressive counterpuncher.