Quite a lot of them, really. Thomas Aquinas, for example, provided and still provides an excellent model for anyone who wants to be a debater, because his method is devastating. At first he lays out the opposing side's arguments, even augmenting and strengthening them when he can, before proceeding to poke logical holes in them. That accomplished, he builds up his own arguments based not on analogy, but on the rules of logic as understood at the time and on references to the arguments of other thinkers (usually Aristotle, who was highly regarded by the medievals).
Meanwhile...
Duns Scotus anticipated a lot of modern empiricism by a few hundred years; Roger Bacon was doing science (as a monk, no less) in the thirteenth century. Abelard propagated an ethics which, while building on Aristotle's, was almost modern in its treatment of individual intentions as the key to judging an action. Avicenna gave us the grounding for a lot of advanced logic.
etc., etc.
But, alas, we have a deeply-ingrained popular conception today that those guys were all a bunch of witch-burning troglodytes who must obviously have been our intellectual inferiors, and thus incapable of anything but the caricatures of thought we assign to them.
Meanwhile...
Duns Scotus anticipated a lot of modern empiricism by a few hundred years; Roger Bacon was doing science (as a monk, no less) in the thirteenth century. Abelard propagated an ethics which, while building on Aristotle's, was almost modern in its treatment of individual intentions as the key to judging an action. Avicenna gave us the grounding for a lot of advanced logic.
etc., etc.
But, alas, we have a deeply-ingrained popular conception today that those guys were all a bunch of witch-burning troglodytes who must obviously have been our intellectual inferiors, and thus incapable of anything but the caricatures of thought we assign to them.