http://paulstamatiou.com/2007/07/17/on-being-a-website-performance-junkie/
Interesting article on offloading images to Amazon's S3 service to improve site performance (WordPress in this case).
http://mnm.uib.es/gallir/wp-cache-2/
The WordPress WP-Cache2 caching plugin / platform. The plugin caches WordPress to static files and then serves those files instead of rebuilding the pages on every request.
http://lightpress.org/
LightPress is a fast, template-based frontend for the popular WordPress blogging platform.
http://www.i-marco.nl/weblog/archive/2007/05/27/on_a_quest_for_ultimate_websit
May 2007 - A guide to optimising WordPress focusing on browser led optimisations such as fewer http requests, spreading images over hostnames, and so on.
http://www.earnersblog.com/digproof-your-wordpress/
March 2004 - A general, overview level guide to optimising your WordPress hosting. Covers caching, MySQL, PHP and apache optimisation in general terms.
http://blog.taragana.com/index.php/archive/5-golden-tips-for-wordpress-performance-optimization-slashdot-digg-protection/
April 2007 - A guide to optimising your WordPress hosting environtment focusing on PHP, MySQL optimisations and plugin / caching optimisation.
http://www.connectedinternet.co.uk/2006/06/18/guide-to-optimizing-wordpress-servers/
June 2007 - A guide to optimising WordPress sites, focusing on MySQL and PHP caching techniques.
http://blog.circlesixdesign.com/2007/01/22/diggproof/
January 2007 - A guide to optimising a server for WordPress hosting, focusing on MySQL and PHP caching techniques.