Looking for an online public domain map

I’m trying to find a map I can use in a Powerpoint presentation.
I need one of Japan that I can alter so I can make notations next to particular cities I visited on a trip.

Depending on the level of detail needed, this one might do:

Or some from here:

http://www.lib.utexas.edu/maps/japan.html

The CIA World Factbook has a small one as well that is PD.

Try The National Geospatial - Intelligence Agency (NGA):

It is a portal for available imagery and maps produced by the Federal government. You can download in a variety of formats.