It depends on what you are trying to discover. If you are looking for discussions of battles and tactics I don't have an answer for you. However, if you are wondering about individual combat training (e.g. how to fight manuals) I have heard good things about a few.
Hans Talhoffer's - fechtbuch
Joseph Swetnam - schoole of the noble and worthy science of defense
George Silver - paradox's of defense
Joachim Meyer's - Kunst des Fechten
I know there are more but most sites I would research on are blocked at work. If these are the types of books you are looking for let me know and I will check for more titles tonight at home.