Finding Information on Personal Participation in World War II, a brochure on some of NARA's relevant records, and how to get started.
Missing Air Crew Reports (MACRs)
World War II Honor List of Dead and Missing Army and Army Air Forces Personnel
State Summary of War Casualties from World War II for Navy, Marine Corps, and Coast Guard Personnel
And don't miss the link at the bottom of the page, to the Archives Library Information Center's WW2 page for even more research resources.