The webmaster of this site, like most people, has a very lengthy list of favorite websites.
The following are singled out not only because they have been helpful personally (in learning and writing about naval warfare during World War II), but also because of the quantity and quality of the information, documentation, photographs, etc., found on these sites.
Aviation Enthusiast Corner: Excellent source of information on aircraft (domestic and foreign, historical and modern) and aviation museums.
Historic Naval Ships Association: Site with information on the 180+ preserved U.S. Navy and other ships (located both in the U.S.A. and a number of other countries). Also has an extensive “Knowledge Base” containing manuals, documents, ship plans and other naval information.
Naval History and Heritage Command, formerly known as the Naval Historical Center: The on-line U.S. repository of information on the history and traditions of the U.S. Navy.
NavSource Naval History: The site to visit if looking for photos of the U.S. Navy vessels of practically every class. (Note: this web site sometimes loads slowly, but its extensive content makes the wait worthwhile.)
Norwegian Merchant Fleet 1939-1945: Site contains practically everything one might want to know regarding Norwegian mariners and merchant vessels that plied the seas during World War II.
Plimsoll Ship Data: A site where one can access Lloyd’s Register of Ships data, in particular the volumes covering the years 1930 through 1945.
Royal Netherlands Navy Warships of World War II: Site provides a wide variety of information and photos on Dutch combatants that served in various theaters in World War II.
Researcher @ Large: A site with a variety of information pertaining to U.S. Navy ships and planes that primarily served in the Pacific Theater, though other theaters are covered.
U-boat Archive: One of the two premier sites dealing with the history of German U-boats in World War II, with many photos and records not found elsewhere on the web.
Uboat.Net: The other premier website that provides a wealth of information about German U-boats (that operated in World Wars I and II), the officers and enlisted men who served aboard the U-boats, the merchant vessels that they attacked, and the naval forces that opposed the U-boats.
WW II Resources: A great site for locating a wide variety of primary source materials on WW II.