Encyclopedic Websites:

American Military History, volume II, The United States Army in a Global Era, 1917 – 2003 (Army Historical Series, Richard W. Stewart, general editor)
 http://www.army.mil/cmh-pg/books/AMH-V2/AMH%20V2/index.htm

Aerial Reconnaissance Archives, The
http://www.evidenceincamera.co.uk/
This site aims to make available the aerial reconnaissance photographs taken over occupied Western Europe by the Allies during World War II.

Documents of World War II
Prepared by Vincent Ferraro, The Ruth C. Lawson Professor of International Politics, Mount Holyoke College.
http://www.mtholyoke.edu/acad/intrel/ww2.htm
Contains an extensive list of documents by key officials (including speeches, broadcasts, telegrams, addresses, letters, orders, statements, resolutions, memoranda, agreements).
The Generals of World War II (Provides the names of a large number of WWII generals, arranged by country).
http://www.generals.dk/bibliography.php

Historical Text Archive: World War II (BBC America Shop).
http://www.historicaltextarchive.com/sections.php?op=listarticles&secid=18
Includes links to personal letters and accounts, as well as articles and papers.

Hyperwar: A Hypertext History of the Second World War
http://www.ibiblio.org/hyperwar/
This is a collection of material related to the (primarily military) history of the Second World War, completely cross-referenced via hypertext links. It includes official government histories (United States and British Commonwealth/Empire); Source documents (diplomatic messages, Action Reports, logs, diaries, etc.; and primary references (manuals, glossaries, etc. Wherever possible, hyperlinks between these histories and documents have been included.
The "Order of Battle" information was compiled by the HyperWar authors. This currently includes pages for each of the ships in the U.S. Fleet; a start on pages for U.S. Army Divisions; and a smaller start on pages for U.S. Marine Corps Divisions.

Pacific Theater (organizational chart).
http://www.ibiblio.org/hyperwar/USA/USA-P-Strategy/charts/USA-P-Strategy-3.jpg
(print the chart to view it clearly)

Planned Command Arrangements for Overlord (organizational chart).
http://www.army.mil/cmh-pg/reference/normandy/TS/MD/notes/158.jpg
(print the chart to view it clearly)
Strategic Planning for Coalition Warfare 1943 – 1944 (Center of Military History, United States Army, prepared by Maurice Matloff).
http://www.army.mil/cmh-pg/books/wwii/sp1943-44/bib.htm
The U.S. Army in the Second World War (insignias). http://webpages.charter.net/usaihp/wwii.html
U.S. Army World War II Corps Commanders: A Composite Biography (U. S. Army Combat Studies Institute, prepared by Dr. Robert H. Berlin)
http://www-cgsc.army.mil/carl/resources/csi/Berlin2/BERLIN2.asp

World War II Links on the Internet (History Department, University of San Diego).
http://history.sandiego.edu/gen/ww2_links.html
Contains an extensive list of links on a wide variety of World War II topics.

Yahoo.com World War II Index
http://dir.yahoo.com/Arts/Humanities/History/
By_Time_Period/20th_Century/Military_History/World_War_II/
An extensive list of links on a wide variety of World War II topics.