Searching through mostly commercial military listings, here are the top ten databases (in no particular order).

These sites are government/military inclined. The purpose for a majority of them are quite commercial, like Geocities or Tripod. An obvious sense of community seems to be the mission of these sites. A good idea, nonetheless. Maybe you will find yourself willing to join and register?

Online militia

Service member search boxes usually reside in the main page, though some exist behind the "search" section. Expect a limited amount of information offered to your query because the Privacy Act prohibits access to other people's address and social security to the public.

To test the validity of these search engines, I use my friend's name, as well as my own. My name is quite different, while my friend's is rather common. (My friend also has government security clearance so he's much more monitored). We both actively joined the service within the past few years. A Vietnam Veteran's name is also tested.

Zap List

• Military.com
  

  A new kid on the block, this place organizes its communities by units. Anyone can join their unit section and find a friend who once shared the same company or battalion. I found my friend by entering his full name instead of just the first and last. I was not there, and when I tried to manually find my name in an alphabetical list, it took too long. I was only told the state, specialty, rank, and duty of my friend's current status.

• Militarycity.com
  

  Have you ever stood in line at the Exchange store and started browsing the headlines of the Navytimes, Armytimes, MarineCorpstimes, etc.? They all fall under one roof at Militarycity.com's site. A Military Registry claims listings of the retired but is either unsatisfactory or is under renovation. Their personnel locator is currently under wraps.

• VeteranSearch.com
  

  Their motto: "We Make Grown Men Cry." Although the site looks amateurish, don't underestimate its contents. Vietnam veterans created and maintain this site committed solely to reuniting old war buddies. It asks for a membership fee in order to get their service for a lifetime. But if you're a disabled veteran on pension, a former POW, or just plain can't afford it, the webauthors will gladly let you in for free. When was the last time you ever saw an honor system at a commercial website? (Excluding shareware).

• Enlisted.com
  

  A community sponsored arena, it has the progressive speed of a turtle on caffeine. Not very fast. I discovered it before I enlisted and it seems to suffer from eternal construction syndrome. They offer forums as means of interactivity and communication. No database search engine found.

• Military-Network.com
  

  Words to describe: Well-rounded. Informative. Unflashy. Okay, so "unflashy" is not a word, but it fits. A surprising amount of content gives it a pleasant filling. 411Locate powers the site's search engine, but requires free registration to develop its database.

• Desert-Storm.com
  

  Simple, yet informative site dedicated to Gulf War veterans. Like the above, it features a by-registration database to run its registry.

• Fredsplace.org
  

  Hey all you Coasties, rejoice! Fred's Place commits to all Coaast Guard personnel and their families by including an email registry and a unit registry. Find Coast Guard members, active, retired, reserve, auxilliary, friends, families, and units. Although not commercial, it deserved a place in our listing.

• GI Search.com
  

  Yet another register database. You or the party you are looking for must register first to become included into the database. Only then can a search commence. The ability to locate names by searching duty stations proves convenient and useful. Free to everyone including non-military individuals. All branches.

• US Navy Directory
  

  The official Department of the Navy X500 Directory. Simple and to the point, but I still can't find my own name. An official using an encrypted government computer has access to Smartlink, "the emerging foundation of a Worldwide Intranet supporting Navy and Naval joint applications."

• Military USA
  

  Boasts 2.7 million Vietnam Veterans in the registry, including over 680,000 for the Desert Storm registry. I tested and located my Vietnam Veteran successfuly—and quickly. Not only does it nurture superb listings, it also provides free services pertaining to reunions, and other veteran activities. Casualties for the Korean War, Vietnam, and Desert Storm are also included. Warning: Active Duty, watch-out, their hard-core database service has a steep price of $50. But to Veterans, the search is free.