-International Driver's License - If you want to drive
-Power here is 50 hz, vs. 60 hz in the US. Make sure all electrical devices you bring support 50 hz power (on UL label)
-Laptop - I am a computer junkie, but would recommend bringing a laptop to everyone. You can lease them through Dell for a reasonable price. The Japanese keyboards are...interesting to use.
-Camera and an obscene amount of film - I brought an analog camera with me. I decided to import a digital camera after a few weeks. I have been able to take many pictures with the digital camera that I may not have taken with an analog camera. I would recommend using a digital camera, though it certainly isn't for everyone.
-Lots of luggage - I barely fit all my stuff in my suitcases for my departure. Make sure you leave some room for things you will buy when you are here.
-If you like American candy, make sure you bring it. I am glad that I brought Altoids along.