Well, I can give you the American army.
Enlisted:
Private
Private First Class
Non-Commisioned Officers:
Corporal
Sergeants (I forget how it goes, Staff, Technical, Master, Chief Master...?)
Officers:
2nd Lieutenant
1st Lieutenant
Captain
Major
Lieutenant Colneol (sp?)
Colneol (sp?)
Generals:
Brigadier is one star
Major is two stars
Lieutenant is three stars
(??) 4 stars
(??) 5 stars (we haven't had a 5 star general since Ike, or was it Marshall?)
The British are similar to the Americans, but they have some other ranks like Lance Corporal (I think the Americans adopted this, I'm not sure)
The German military is similar to the American military. I only know a few ranks, though: Feldwebel is Sergeant, Oberfeldwebel is Lieutenant (I think?), Hauptmann is Captain, Oberst is Colneol, and Field Marshall is Feldmarschall.