To find a person or leave information about someone who is safe:
http://japan.person-finder.appspot.com/?lang=ja
For maps, links to blogs, Twitter, news, emergency telephone numbers and more:
http://www.google.com/crisisresponse/japanquake2011.html
Note that each page can be translated into English or Japanese by clicking on the appropriate language box at the top of the page.
If you want to donate to relief efforts, here’s a list of recognized organizations:
http://www.huffingtonpost.com/2011/03/11/how-to-help-japan-earthquake-relief_n_834484.html
We have a nephew living in Japan and are happy to report he has checked in via Facebook and, so far, is fine.