General Military Information:

Military Public Affairs & Department of Defense Information: http://www.defenselink.mil
Provides one stop shopping for basic information regarding the United States military, to include photos, news stories, official announcements from DoD leadership, and many other useful links for research.

Military Rank Information and Comparisons: http://www.defenselink.mil/specials/insignias/officers.html
Provides information regarding officer and enlisted ranks for the various branches of the U.S. military.

DoD Dictionary of Military Terms: http://www.dtic.mil/doctrine/dod_dictionary/
From this page you can browse the DOD Dictionary of Military and Associated Terms. The DOD Dictionary and the Joint Acronyms and Abbreviations master database are managed by the Joint Doctrine Division, J-7, Joint Staff.

Military.com: www.military.com
Provides many resources and information on just about anything related to the U.S. military. This website is run by veterans for veterans. It is very user friendly and easy to navigate.

Stars & Stripes: http://www.stripes.com/
Stars and Stripes is a daily newspaper published for the U.S. military, DoD civilians, contractors, and their families. Unique among the many military publications, Stars and Stripes operates as a First Amendment newspaper, free of control and censorship. Stars and Stripes maintains news bureaus in Europe, Pacific and the Middle East to provide first-hand reporting on events in those theaters.

Military Times Media Group: http://www.militarycity.com/
Military Times Media Group is the source for military news and information servicemembers have trusted for over 60 years. Every week, the print edition of the newspapers, Army Times, Navy Times, Air Force Times, and Marine Corps Times, deliver exclusive, original, in-depth news and analysis about career, pay and benefits and issues impacting professional advancement. In addition to this vital career news, each paper is packed with community information and active lifestyle features of interest to military personnel and their families. The Military Times papers offer over 18 supplements throughout the year, including valuable military resource guides, a special annual historical issue, military healthcare specials and important second career and educational supplements. 

Military Success Resources from Answers.com http://military.answers.com/