Well, our time is drawing to a close and this means sending things back to the USA in our case. I thought it might be useful to share some of the things we have found.
Option 1: the post office
If you don't have a lot of stuff the post office is a good option. They have a very good English site and several different shipping options. Here is their rate schedule. If you are sending a lot of books, using a special mail bag might be a good option. Be sure to pack carefully though if you use the boat route- I had some minor damage from a breaking box on an earlier package. This can only be done at the central post office near the station or the Sakyo post office.
Option 2: shipping companies
These are usually based on the cubic meter and go by boat. Good for larger amounts of things. You can often choose to send it to your door, or for a cheaper route they can send it to a port near you. This does not mean that it has to be near an Ocean. I sent stuff to Detroit before. Here are some basic prices to the USA for your reference.
A friend used Economove. They quoted me about 75,000 JPY to the east coast of the USA door to port. They give you a big box to send things in.
We have use Japan Luggage Express before and were pretty happy with it. They quoted me about 60,000 to the east coast USA. For this one you don't get one big box, they just add up the dimensions of your packages (one cubic meter is a lot!).
I had another recommendation for Kuroneko Yamato, the ubiquitous takkyubin. (Sorry the information is only in Japanese) For door to door service they have about .7 cubic meter for 75,000 to the west coast, New York of Chicago or and 110,000 for the rest of the USA. From what I hear this is a very nice option.
Anyway- I hope this helps. This time I think we will go the regular post office route.