The collapsing categories plugin creates a list of all categories, subcategories, and posts, which can be expanded and collapsed dynamically, as you can see in the sidebar on this page.
The plugin is hosted on the official WordPress repository at: http://wordpress.org/extend/plugins/collapsing-categories
If you have any questions, bug reports, or feature requests, please visit the Frequently Asked Questions, and at the other comments here (find is your friend)).
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