Can we assume that you have done all the basic design things like optimising images, ditching massive background graphics and generally removing bloat from the code?

Then what are the specific issues that are causing you to want to squeeze that last bit of performance out of the site? Massive traffic? Customers in areas with slow connection speeds?

Try a caching solution. Memcached is what I use.

Another criteria is user experience. If you are slower than your toughest (and/or faster) competitors people will start using the back button. Google is now favoring pages that load fast according to recent Google blog posts.

Due to the recent economic changes there has been a growth in dialup usage (dumping costlier high speed). Check your site and your competitors on 28k dialup. Page rendering wobble is magnified at slower delivery times. Is your page as viewable mid load as your competitors? Ask friends you trust to do this testing as well.

just get top grade on pagespeed and yslow.
if still too slow - remove some parts of the page. Webmasters often put too much garbage on pages to have more "features". But they are often useles.
if still too slow - use content delivery network.

All the above mentioned plus
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