If you spend a lot of time on Xbox 360 playing Call of Duty or Halo, you may have a decent handle on the US Military Ranks for Officers and Enlisted for one or maybe two branches of service. However, you can't rely on "gamer cred" to help you remember all of the ranks for all of the US military Service branches.
Here are some rank insignia charts for the United States Army, Air Force, Navy, Marine Corps, and Coast Guard. Learn 'em. It's good to know who your wife salutes or who has to salute your wife.
(Oh, and gamers don't look for those high ranks and insignia that you see in Call of Duty. They're not real.)