Matt,
The best thing about history from this period is all of the new histories that have appeared the past twenty years or so and continue to appear. I would recommend Jonathan Sumption's four volumes first. They are broad and focus on political, economic and social issues as much as the military-but if you are really interested in Breton politics and the perpetual strife there, only Sumption follows it.
If you're looking for something beyond the Osprey Campaign books-all of which are fine, though some are a little dated-these are some interesting titles.
Crecy-Livingtone and Witzel's "Road to Creccy" is quite good and covers the entire campaign. It's a great read. Kelly DeVries and Michael Livingston published a collection of essays and primary sources "The Battle of Crecy: A Casebook" Andrew Ayton's collection of writing on the battle from 2005 is also quite useful. DeVries and Ayton both question our traditional understanding of where the battle was fought.
Poitiers-David Green's "Battle of Poitiers: 1356" is a fun little book and written with wargamers in mind. Includes OOBs. Christian Teutsch "Victory at Poitiers" takes another look at the battle and offers some interesting and different conclusions from accepted norms. If you can find a copy of the old Knight's Games series "Poitiers 1356" by Donald Featherstone, it's worth a look. Probably set you back about ten bucks.
Agincourt. There's a split between historians on Agincourt now. The traditionalists would be Alfred Burne and Juliet Barker who embrace the Band of Brothers version portrayed in Shakespeare's Henry V. Anne Curry's "Agincourt: A New History" from 2009 changed all that with a stronger Henry V and a much reduced French force.
Bottom line is there are lots of great books, new re-examinations of the period based on new sources. Lots more available than I've included. Can't help you much with non-English language sources. Good Luck
Kevin
