A plugin for magento that is meant to boost performance. Free.
Very useful article outlining the broad basics of optimising Magento. Includes links to more detailed information and lots of config file examples. Very useful.
Very detailed article explaining how Magento implements its caching mechanism. It seems to be some custom classes layered on top of Zend's caching framework. Useful read.
Using APC (Alternative PHP Cache) and WP-Cache2 together causes some issues, the solution is to have APC not cache the wp-cache-config files.
June 2007 - A guide to optimising WordPress sites, focusing on MySQL and PHP caching techniques.
January 2007 - A guide to optimising a server for WordPress hosting, focusing on MySQL and PHP caching techniques.