Here is the link to the irs website.
http://www.irs.gov/formspubs/page/0,,id=12236,00.html
Emperor is right. As a general rule, you owe U.S. tax even on foreign earned income. But there are exclusions and deductions if you paid tax on the income in the foreign country and their are foreign housing deductions. But I would think this would only help you if you pay a high tax or have expensive housing costs in the foreign country.
Anyway. Take a look at the IRS general info on this.
Interesting question.
Was actually surprised by the correct answer. I had always heard that people working overseas in Saudi Arabia or Japan did not owe U.S. income tax.