BBC - The Great War at Home (U.K.) - BBC (British Broadcasting Corporation) radio, video productions and commentary, including many primary sources.
Britain 1906-1918: Contrast, Contradiction & Change (The National Archives, U.K.) -- "Civilians & War 1914-18", and "Propaganda 1914-18"
The Cabinet Papers 1915-1986 -- includes discussions among Cabinet members about the war.
The First World War: Sources for History (The National Archives, U.K.)
The Great War Archive | The First World War Poetry Digital Archive (Oxford U.) -- this web site contains two archives: archival items from World War I, and World War I poetry.
The Great War: 1914-1918 (The National Archives, U.K.) - official site from the National Archives; wealth of information in varied formats.
Imperial War Museums
The Map as History: Europe after World War I -- very well done animated map with commentary showing boundary changes after the war. (rest of maps require subscription)
National World War I Museum and Memorial (US)
Spartacus Educational (U.K)
The Wall Street Journal: World War I Centenary: 100 Legacies
The Western Front Association
World War I: Trenches on the Web
Best of History Web Sites - WWI
History.com: World War I -- videos and articles from History.com
Internet Modern History Sourcebook -- World War I; Some links overlap and some are broken but it is still worth looking around this site.
United States Holocaust Memorial Museum: Treaty of Versailles
World War I in Photos (The Atlantic)
Upper School Library eResources
MLA Formatting Guide
Citing Primary Sources: MLA
Annotated Bibliography Guide