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

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