I have written more than a few articles detailing how to improve the speed of a website, and due to popular demand, this post will detail all the latest and greatest caching tricks and techniques that I utilize and love. The AskApache Best-Practices.
Optimization
If you desire SPEED from your WordPress blog, the #1 speed improvement comes from using the WP-Cache Plugin. If you still desire SPEED after installing the Plugin, you can modify the WP-Cache Plugin code to make your blog even faster!
Optimization Cache wordpress WP-Cache

3-Part article covering practical implementation of 3 advanced .htaccess features. Discover an easy way to boost your SEO the AskApache way (focus on visitors), a tip you might keep and use for life. Get some cool security tricks to use against spammers, crackers, and other nefarious sorts. Take your site's error handling to the next level, enhanced ErrorDocuments that go beyond 404's.
Htaccess SSI
I looked at a lot of different ways to display quotes and pullquotes and even though the javascript solutions are very nice, esp. the 456bereastreet.com solution, I decided to just use CSS (Keep It Simple Stupid).
CSS
We've figured out what mod_rewrite variables look like, a cheatsheet of the actual value.
Htaccess Apache cheatsheet Htaccess htaccess file mod_rewrite PHP rewrite Rewriting

Well what can I say, other than this is sooo DOPE! Here is a list of the modules this plugin (version 4.7 unreleased) will automatically detect. I compiled the list myself using every module included with any default Apache installation for ALL the versions listed below, 1.3 to 2.2+
Want to know something else I'm including in this plugin? For each and every module that is detected, this plugin can then detect ALL of the modules .htaccess Directives! For instance, RewriteRule, AccessFileName, AddHandler, etc.. are each a directive belonging to a module that is allowed to be used from within .htaccess files.
Talk about sick.. these tricks have the diamond disease!
WordPress Advanced Anti-Exploit Anti-Spam Htaccess RewriteCond RewriteRule security SSL THE_REQUEST
This article shows how to save and modify php session data, cookies, do anything really... without using ajax or iframes or forcing the user make a request.
PHP
Host Google Analytics ga.js file locally for increased speed! Makes web pages load faster.
Google
Google AdSense calles their AdSense Ads, "Sponsored Links", while Text-Link-Ads.com recommends "Sponsored By". Of course it is against the Google Adsense TOS to rename your ads, but in general, for non-adsense, what do you like to call your sponsored links?
SEO