I'm looking for information about an American POW (Prisoner of War) at Stalag Luft 1 in Germany during World War II. What free records of pilots/POWS, etc. are available online?
The German Red Cross also maintains a WWII tracing service that works independantly from the ICRC services. They have their own records (I confirmed this via email), which indicates that they may even in some cases have information that the ICRC doesn't.
The International Red Cross holds a lot of information about POW's from WW2. They are currently digitising all their records. At the moment you have to make a written application for them to conduct a search and as a result the response from them can take some time. I did some research on my Father-in-law with them. It took about 3 months from when I applied to getting the answer but it added to our knowledge of his war service. See this link for more details on how to apply for the information.
As there is unlikely to be more detailed information about your person of interest on line, to learn more about his time in the camp, you may find it rewarding to research it more generally -- B24.net or Merkki.com may be good starting points.