The following plugins can boost your joomla site's performance greatly.
Plugin Google Ajax Library can host Mootools(70K),Prototype,JQuery,YUI libraries, which can save bandwidth and speed up your site's response.
Tips:This plugin is suitable for all joomla site.
Tips:This plugin is suitable for most joomla site.
Plugin Phil Taylor's SPEED UP your Joomla Admin Console can use Google Gears to speed up your Joomla administration.
Tips:This plugin can only speed up your administration, can't speed up your front side.
Plugin Content Static can convert your joomla site into html static files, which saves the need for costly SQL resources to load pages from a database.
Tips:This plugin can boost your site mostly, however it doesn't work with vote,reviews etc.
If you use all of the plugins, please notice the order of them. They should have the following orders: Google Ajax Library < CssJsCompress < Phil Taylor's SPEED UP your Joomla Admin Console < Content Static(From low to high).