http://www.jpo.go.jp
http://www.ipdl.inpit.go.jp/homepg_e.ipdl
http://www19.ipdl.inpit.go.jp/PA1/cgi-bin/PA1INIT?
http://aipn.ipdl.inpit.go.jp/AI2/html/top.html
http://aipn.ipdl.inpit.go.jp/AI2/cgi-bin/AIPNSEARCH

The Japanese Patent Office provides the following searching services in English

Searching of PAJ (Patent Abstracts of Japan) (English)

And the following services in Japanese
Searching Patent Gazette,
Searching Front Page of Unexamined Patent Gazette,
Searching Japanese Trademark Database

The coverage of the PAJ is (Publication Number) from JP05000001 to JP10113000.

Text Search allows the searching of the following fields, Applicant, Title of Invention, and Abstract. The search is limitable by IPC marks and publication dates. Number searching is possible as well.