Also, Google books has done an excellent job of scanning a huge amount of material that covers the period in English, French and German. Archive.org is also an excellent site for finding out of print/out of copyright materials. Here's one that is a classic: Sir Julian Stafford Corbett - England in t...

Kronoskaf's list is growing well. Lots of free titles/pdfs/ebooks by eminent historians. Also a lot of contemporary works on the subject. Some of the German works were translated into English and French. This is my first post, so I can't post the link, but it is easy to find in Google. Just type "kr...