Financial planning resources for U.S. expatriates?

What are some good resources to help an expatriate plan for retirement? I anticipate spending most of my life living outside of my country of citizenship (the United States), specifically in Japan. I'm reaching the point where I need to begin thinking about financial planning, particularly saving for retirement. I'm aware of how to do this if I were resident in the U.S.; however, I'm very unclear on the particulars of doing so as an expatriate. Much of what little I have found on the Internet or in books is grossly out of date or vague. Can you recommend any books (websites are also okay, but I'd prefer something something well-written and well-sourced) intended for expatriate Americans who want to begin saving for their retirement? First-hand advice or experience would also be welcomed. I realize that I should talk to a financial planner, but at the moment that's putting the cart before the horse; I just want some general advice on my somewhat unique situation. (FYI: I have read this recent thread as well as many others in the archives. I am not interested in advice about living abroad, only managing my finances and planning for the future while in a foreign country. Personal inquiries or off-topic comments are welcomed via email. Thanks in advance.)