WordPress.org

This Plugin adds a Flex Accordion Navigation to your wordpress instance. This plugin is perfect for those sites that have out of control links in the sidebar. With Flexible-Navigation you can simply use one function call in the sidbar to generate an accordion navigation from your links, posts and catagories.

With some modification you could use this plugin to wrap each posts content in an accordion.

To view a demo of what this navigation might look like visit: http://www.dreamwagon.com/flex/examples/accordionupdate/index.html.php