"IWM is unique in its coverage of conflicts, especially those involving Britain and the Commonwealth, from the First World War to the present day. We seek to provide for, and to encourage, the study and understanding of the history of modern war and 'wartime experience'."
"A site all about the soldiers, units, regiments and battles of the British Army of the First World War, and how to research and understand them." Run by an amateur historian, but has useful general information and research tips.
The Canadian Military Heritage Project. "This is not the entire story of World War 1, but an overview of Canada's role in this terrible conflict which cost the lives of more than 56,500 Canadian soldiers."
Diary of Albert Huet, a French soldier, written after the conclusion of the war that describes his experience during the war. Digitized original with transcriptions.
"Full-text searchable transcriptions of letters, speeches, notes, and other documents are available, as well as scans of original manuscripts and images. Documents and images are added daily."
"The portal enables researchers to explore by means of a website the documentary materials found in the archives of Hungary, both those involved in the cooperation and those which will join later. In order to the increase the efficiency of the research, a unified database has been created, and the content is continually being expanded." The site is available in Hungarian, English, and German.
An overview of issues and things to keep in mind when looking into Austro-Hungarian military records. Contains images and examples. This website appears to be very sporadically maintained.