Sites offering statistical information about Japan's government, economy, and international relations that can be accessed conveniently in English.

National Diet Library, "Statistical Materials for Learning About Japan." A good first stop for any Japan-related statistical needs. The introduction provides at least as much detail as needed to use the 19 headings of the "Contents" section at the bottom of the page. Links are provided throughout for web-based sources of data.
The Portal Site of Statistical Data in Japan. Some pages of this site are still under construction. But the economic and social statistical information available is comprehensive and well organized. Everything from simple graphical representations to detailed explanations of how Japan collects and presents statistical information is included. Be sure to scroll down to the "Links to Statistical Agencies" section in the lower left of the home page, as well as the categorical headings on the right-hand side.
Statistics Information Site of the Cabinet Office's Economic and Social Research Institute. This is a good site for current business and economic statistics.