You may find that you desire functionality and there is no plugin that anyone knows about that performs that functionality. It's probably best at this point for you to either pay someone to write the plugin you need or write it yourself.
Plugins are pretty easy to write and can cover a lot of really different functionality. The best way to learn how to write PyBlosxom plugins is to read through the plugins in the plugin registry. Many of them are well written and may provide insight as to how to solve your specific problem.
Additionally, feel free to ask for help on the pyblosxom-users and pyblosxom-devel mailing lists.