Note to self: The gnu talkfilters package at
http://www.dystance.net/software/talkfilters/ contains a bunch more
filters, as well as probably some updated versions. I should see about
integrating this into filters. As a first step, I have mailed its
maintainer. If nothing comes of that, I may want to add selected ones
into the filters package.

I am slightly unsure of some of the copyrights of various of the
talkfilters. They seem to have just taken them and slapped the GPL on
them if they could not contact the author:

   While all of these filters have been available in one form or
another in the public domain for many years, the original authors of
some of the filters are unknown. Reasonable attempts were made to find
the authors and obtain written permission to repackage the filters as
GNU software, but in some cases they could not be located.