The Army Air Forces of W.W.II generated a lot of paperwork. Many of these records exist today in their original form or on microfilm and microfiche. These records are maintained at a handful of facilities around the country.

• Personnel records - these records are maintained by the National Personnel Records Center, Military Personnel Records in St. Louis Missouri. Unfortunately a fire in 1973 destroyed many records, but you should always start here. If you are not a family member you will be prevented by the Privacy Act of 1974 in the amount of information you can obtain via this source.
  
  
  • Records request can now be made online if you are the veteran, or the next of kin of a deceased veteran. Next of kin is defined by the archives as; surviving spouse that has not remarried, father, mother, son, daughter, sister, or brother. - [vetrecs.archives.gov]
    
    
  • National Personnel Records Center, Military Personnel Records: Link to SF-180 and other information you'll need.
     
    A note from NPRC on delays: "Response times for records requested from the National Personnel Records Center (NPRC) vary greatly depending on the nature of the request. For example, the NPRC Military Records Facility currently has a backlog of 180,000 requests and receives approximately 5,000 requests per day. Routine requests for separation documents currently require only 2-4 weeks for servicing. However, requests that involve reconstruction efforts due to the 1973 fire or older records which require extensive search efforts may take much longer. The average turnaround time on all requests is currently running at approximately 12 weeks".
    
    
  • Alternative Source -- County Courthouse -- after WWII a lot of servicemen were encouraged to store copies of their separation papers at their local county courthouse. It's a long shot, but one that has paid off in a number of cases.
    
    
• 293 file, Individual Deceased Personnel File - this file is maintained by the Department of the Army in Washington, DC. If the veteran you are researching was Killed in Action you will definitely want to obtain this file. This file documents the activities of the Graves Registration Command and the Army to locate, identify, and provide a final resting place for the deceased.
  
  
  • The U.S. Army Personnel Command handles these requests.
    
    Mailing address 
    
    U.S. Army Personnel Command, Public Affairs Office (FOIA)
    200 Stovall Street
    Alexandria, VA 22332-0404
    
    Enclosed in the letter the requestor should cite the Freedom of Information Act (FOIA) and provide full name of the relative, service number, and date of death (or whether the death was during WWII, Korea, or Vietnam). 
    
    Return mailing address is required. Please allow up to 20 weeks for the research process. FOIA fees are waived for requests from family members for death/burial records on their loved ones.  

• Missing Air Crew Reports (MACR) - if your research involves the loss of an aircraft in a combat situation and not in Allied territory, the MACR will be invaluable. This document was generated shortly after the loss of the aircraft (usually within a day or so) and lists the crew roster, aircraft, and basic details of the loss including eye witness statements if they were available. ArmyAirForces.com has a fairly complete index of MACRs which may aid you.
  
  
  
  • These records are maintained by the National Archives and Records Administration II in College Park, Maryland. Over time, the MACR report became a file, containing a collection of documents relating to the aircraft loss. You should request the entire file.
    
    Mailing address
    
    National Archives and Records Administration
    Textual Reference Branch
    8601 Adelphi Road
    College Park, MD 20740-6001
    
    
  • NOTE: most 15th AF records are stored at AFHRA, Maxwell AFB (see below) instead of the National Archives. 

• KU Report - National Archives and Record Administration (NARA). If the loss of the aircraft occurred over German territory, a German Kampf Flugzeuge USA [Battle Planes USA] document was prepared by the Luftwaffe concerning the location of the aircraft wreckage and fate of the crew. National Archives has the original reports as well as translations available. I know of no Japanese equivalent - [See NARA address above].   

•  POW Questionnaire - National Archives and Record Administration (NARA). If crew members survived the loss of the aircraft and were captured and interred by the Luftwaffe. There may be a brief questionnaire on file filled out after the crew member was repatriated to Allied Control - [See NARA address above].
  
  There should be an equivalent document for POWs held by the Japanese.
  
  
• World War II Prisoners of War Data File - these records identify World War II U.S. military officers and soldiers and U.S. and some Allied civilians who were prisoners of war (POWs) and internees. (Select the orange "Search" button, then "Wars / International Relations: World War II" link, Records of World War II Prisoners of War, created, 1942 - 1947 "Search" button). You can enter a search term right away if you know what terms to search for, or I suggest clicking on the "Search" button link for more detailed search options.
  
  
• Accident Reports - sometimes difficult to locate, maintained by the Air Force Historical Research Agency (AFHRA) on microfilm. An accident report can run from just a few pages to a half dozen or more pages and may even include photos of the accident - [see AFHRA address below].
  
  
• Unit Histories, War Diaries, Daily Reports, Station Memorandum, Special Orders, Public Relations Reports, Loading Lists, etc. - these unit documents are archived by the Air Force Historical Research Agency (AFHRA) at Maxwell AFB, Alabama.
  
  You can usually obtain squadron and group historical summaries at no cost through written request. You should also be able to obtain a specific monthly squadron diary upon request. A larger request, say for the entire War Diary, would probably necessitate a copying fee.
  
  You can order Group & Unit microfilm at $30.00 a roll from AFHRA. The microfilm rolls are usually divided up between Group histories, Squadron histories, and tenant command histories. You can e-mail AFHRA to obtain the roll numbers for your unit.
  
  
  
  • Air Force Historical Research Agency (AFHRA): Located at Maxwell AFB Alabama
    
    Mailing address
    
    AFHRA/RSA
    600 Chennault Circle
    Maxwell AFB, Alabama 36112-6424
    
    
  • Air Force History Support Office (AFHSO): Located at Bolling Air Force Base, Washington, D.C. In conjunction with the Air Force Historical Research Agency (AFHRA) at Maxwell Air Force Base, Alabama, which is the primary repository of historical information, the office responds to requests for information from private organizations, government agencies, and the general public.
    
    Mailing address
    
    AFHSO/HOS
    Reference and Analysis Division
    200 McChord Street, Box 94
    Bolling AFB, DC 20332-1111
    Phone 202-404-2261
    
    
• Veterans Administration - the VA handled claims by the families of those KIA. You can write and obtain the VA's file on your claim. If your veteran made any VA claim in the postwar period there is a record of that as well (benefit claims, etc.).
  
  
  • To obtain records relating to your veteran and the VA you can submit a Freedom of Information Act (FOIA) request. Read more about it here.
    
    
  • Department of Veterans Affairs (VA): The VA has procedures to help you find surviving service members. There is no guarantee that this will work, but it's a good resource. The procedure is for you to write a letter to the service member, place that in a SASE (Self Addressed Stamped Envelope) which is in turn mailed to the nearest VA office to the person in question. The VA will then try and forward the letter to that person, and it is up them to respond.

American Battle Monuments Commission: WWII Honor Roll, if the veteran you are searching for was killed in action and is still buried overseas he should be listed in this database. Burials in the domestic United States are not covered.

Department of Veterans Affairs: National Cemetery Administration - Nationwide Gravesite Locator, if your veteran is buried in a national cemetery, this database covers almost all 120 of them. Burials abroad are not covered.

WWII POW Database Search at NARA, the records identify World War II U.S. military officers and soldiers and U.S. and some Allied civilians who were prisoners of war (POWs) and internees. (Select the orange "Search" button, then "Wars / International Relations: World War II" link, Records of World War II Prisoners of War, created, 1942 - 1947 "Search" button). You can enter a search term right away if you know what terms to search for, or I suggest clicking on the "Search" button link for more detailed search options.

WWII MIA Database from the Defense Prisoner of War/Missing Personnel Office. DPMO researchers have completed the first electronic listing of Missing Personnel from the Second World War, which is now available on the DPMO website.

WWII Army Enlistment Records, this can be a great way to find a serviceman's serial number and other basic details (Select the orange "Search" button, then "Wars / International Relations: World War II" link, World War II Army Enlistment Records "Search" button). You can enter a search term right away if you know what terms to search for, or I suggest clicking on the "Search" button link for more detailed search options. 

Note: About 35% of the records have a scanning error, these are minor spelling errors so search accordingly. Additionally, about 13% of the available paper records could not be converted for the database.  

Furthermore, these records are for persons who enlisted in the Army, Army Reserves, and Women's Auxiliary Corps during World War II (1938-1946). The records do not include Army officers; however, note that many officers enlisted first and were commissioned later when they finished their training - so you may be able to locate their initial enlistment records.  

World War II Honor List of Dead and Missing Army and Army Air Forces Personnel, indexed by State. This resource is not searchable yet, the information presented online consists of image scans from the NARA publication.

The veteran's hometown newspaper. This overlooked resource can be a huge asset. Dig through those archives and look for notices about service members. The public relations guys in WWII were great about getting notices posed in local papers about local servicemen; when they graduated from boot camp, training phases, were promoted, sometimes even in action overseas - it's worth your time.

Social Security Death Index at Rootsweb.com, FamilyTreeMaker.com, FamilyTreeLegends.com, FamilySearch.com, search these online indexes for likely matches.  However, note that deceased WWII veterans most likely didn't have SSNs.

World War II records held by NARA, nice overview of the NARA holdings.