Footnote.com has announced that it has digitized the entire Project Blue Book, which is a collection of official records covering government investigations of UFOs, 1947-1969. It’s available for free at http://www.footnote.com/.
You can http://www.footnote.com/browse.php#6283401 browse the information or do a keyword search. I did a search for aluminum and got over 300 results. The results are presented in images of scanned pages, with keywords highlighted. The results I saw were mostly memos of UFO spottings and the conclusion that folks were seeing aircraft.
Frankly I have no idea what to search for in a UFO archive — not really my specialty. So I did like the fact that Footnote allows people to comment on and annotate interesting documents. So you can not only keyword search and browse the total collection, but also browse highlights. Scanned documents have a place to add comments about documents as well as annotations to the documents themselves.