There has been a lot of comment and even Senate hearings about Bush's plan to use military tribunals to try terrorist suspects. It can be argued that these suspects, especially the ones captured in Afghansitan, are prisoners of war. If that's the case, then there is historical precedent for trying them in military courts.

During WWII, thousands of German POWs were held in the US. If they broke the law, they were tried in military courts. The History Channel did a program last year called "The Last Mass Execution in America", based on a book of the same title as listed on Amazon.com. Several German POWs were tried and executed for killing a fellow prisoner in one of the POW camps.

The Japanese War Crimes trials of 1946-48 have been criticized by some, but at least according to this book, the trials were legitimate and laid the foundations for what constitutes war crimes.

POW trials in military courts wasn't limited to the US, either. According to this site, Australia did the same thing. The link on the reference didn't display much information but it does indicate such records exist.

There's also the Canadian Law Concerning Trials of War Criminals by Military Courts. I don't know the current British law on this subject, but they've also used military courts to try accused war criminals.

This practice of trying prisoners of war in military courts dates back at least as far as World War I, as quoted here:
A Royal Warrant for "the Maintenance of Discipline among Prisoners of War "was signed on 3rd August, 1914:

"Whereas We deem it expedient to make regulations for the custody of and maintenance of discipline among prisoners of war interned in the United Kingdom or elsewhere; Our Will and Pleasure is that the custody of and maintenance of discipline among prisoners of war interned in the United Kingdom and elsewhere shall be governed by the laws and customs of war and the regulations attached to this Our Warrant, which regulations shall be the sole authority on the matters therein treated of."

The regulations referred to provided for the establishment of "Military Courts "(as distinct from Courts Martial) , which had power to try any prisoner of war upon "any such charge or charges as may be preferred before them for any offence which, if committed in England, would be triable before a Civil Court of Criminal Jurisdiction, or for any offence the commission of which shall be held prejudicial to the safety or well-being of His Majesty’s Dominions, armed forces, or subjects, or to the safe custody, control, or well-being of any prisoner of war."

In the case of the Prisoner of War Camps in the Isle of Man, the Lieutenant-Governor was appointed the Authority to convene Military Courts and to confirm the proceedings of such Courts. During the existence of the Camps in the Island, 345 prisoners of war were tried by Military Courts and convicted.

I suspect the same practice is true in many other countries. I have not had time to review all of this, but this reference from the Yale Law School appears pertinent to the discussion. So does this article on military force and justice.