There is a downloadable tool bar for Internet Explorer (unfortunately not
yet for Mozilla Firefox), containing a lot of useful links for sources and
archives and journals related to history, particularly Bavarian history.
It's for German speakers, but maybe someone can adapt it for others?
For Firefox users, I'd recommend to check the links one by one on:
http://www.datenmatrix.de/projekte/hdbg/toolbar/hilfe.shtml
Michael