Barded Fury is a set of early Renaissance rules from the Ambler Gamers. You can get them from their Yahoo Group.
The Junior General offers a set of rules — and paper ships — for the 1571 battle of Lepanto.
David Heading offers a set of Renaissance Naval Rules.
Italian Wars is a set of free wargames rules for games set in the Renaissance.
Hot Trod and Red Hand is a set of free wargames rules for sixteenth century Anglo-Scottish border warfare.