Steve Rude on the Cache Router module
Steve Rude talks about the Cache Router module, which is an engine to be able to combine and swap in and out different caching techniques like: APC, Database caching, eAccelerator, File caching, Memcache and XCache.
Some performance tuning tools mentioned are: Navicat, MySQL Top, xdebug, devel module, Firebug and YSlow
For more information on Drupal caching, check out John VanDyk's Drupalcon presentation Inside Drupal Caching: From Static Variables to Memcache