Web Developers sometimes use file.ext?v=004 as a version control system to force visitors to use updated files. This is terrible. Instead link to apache-003.css and set it to be cached forever. When you change the file you just change the links to apache-004.css. That eliminates millions of bandwidth and resource robbing If-Modified-Since requests.
2 awesome ways to implement caching on your website using Apache .htaccess or httpd.conf. Both methods are extremely simple to set up and will dramatically speed up your site!
Example use of an image sprite with css to speed up your websites drastically. An image sprite is 1 image composed of multiple images, using CSS you can display just one part of the image using background-position.
To speed up the site I created a very small swf to pre-cache flv files specified in an XML file. Basically by using the NetStream.play actionscript to start and then stop the playing of an flv file, which causes the flv file to be cached. Uses combination of htaccess, css, xhtml, javascript, actionscript, and xml.
(Est setup time = 4min)