Year ago I was happy to announce the publication of a Finnish open data guidebook (Poikola, Kola, Hintikka 2010) which was published by the Finnish Ministry of Transport and Communications. Now little shorter version is translated into English.
The guidebook is mainly targeted for the civil servants willing to open up the public sector data, but it can serve other audiences as well. Later on I will contribute some content to the http://opendatamanual.org/ -initiative.
Enjoy reading: http://www.scribd.com/doc/57392397/Public-Data-Www