Links on this page are to online research websites. The organizations that maintain these sites have no publication component available. Unless otherwise stated, it can be assumed they are free of charge.

globalsecurity.org
globalsecurity.org is a good resource for DoD program history. Updates are infrequent, but it provides excellent descriptions of how a system/weapon works, who the prime contractor is, who the end customer is, what the outlook of the program was at the time of the last update (pay attention to update dates, some are a few years old!), and the history of the program. The site also provides industry news about topics of interest to them. The researchers are recognized by the media as prime sources for weapons and system information.

fas.org
fas.org is similar to globalsecurity.org because the same person created the bulk of the material at both sites. fas.org is maintained by a non-profit organization called the Federation of American Scientists. Again, a good place to go for program history and overviews.

Army Fact File
The Army Fact File is a little lean on the surface, but incredibly deep if you follow the "Amry A-Z" link. Look for program descriptions, overviews, contractors, etc..

Navy Fact File
The Navy Fact File is very good. Excellent coverage of aircraft, missiles, and stuff I look for. Not in-depth, just a quick 1-page summary of the program.

Air Force Fact File
The Air Force Fact File is also very good, with good coverage of programs.

USMC Major Acquisition Programs, 2003
Up to date, focused on major programs. Some broken links, however.

Defense Daily Network - Program Profiles
It looks like they just took the fact files above, verbatim and put their own letterhead on them.