I'm sure I'll be posting more about the Great War as we approach all the major anniversaries, but for now a couple of resources for writers and historians:
The British Library has just launched a major new website on the First World War, with articles by present day historians and collections of resources from the time. The War is addressed from a European, not just a British, perspective, and the resources are drawn from various countries and are in various languages.
The BBC also has a First World War site where there are articles by present day authorities on various aspects of the war and links to and transcripts of radio and television programmes on the subject. (People outside the UK may not be able to access the television programmes.)
In addition, First World War.com is an established site that's well worth a visit, especially for its collections of contemporary source material.
The late and greatly missed military historian Professor Richard Holmes made two television series of War Walks, which are available on YouTube. The first series included episodes on the battles of Mons and the Somme.