PBS
Bombers of World War Ii: Last Flight of Bomber 31
Website that chronicles the story of the search for remains of Bomber 31 that went down in Kamchatka during World War II. There is also a slide show and descriptions of several World War II bombers.
Other
Dave's Warbirds: American Aircraft of World War Ii
This site from Dave's Warbirds has pictures and information about virtually every American aircraft used in WWII. Look up aircraft by manufacturer, type/function or name.