The NSA has organized a list of security guidelines for multiple operating systems, however, it has started providing the vendors guidelines for newever versions of operating systems when they exist. If you are just interested in what the NSA published themselves, look at the guides for RHEL 5, Windows 2000, Mac OS 10.3 (Panther), and Solaris 8.

http://www.nsa.gov/snac/downloads_os.cfm?MenuID=scg10.3.1.1