The Scot and Welsh Wars is a set of free wargames rules for medieval battles circa 1277.
One Monk offers a set of paper medieval buildings and paper medieval figures.
Lord Merlin has a set of free wargames rules for large (70mm or 1:20) scale figures. There are three levels to this skirmish rules set: "simple", "better" and "more realistic." There also are some cute pictures of a "knights of the dinner table" game.