Asvin Balloo has posted a quick look at making the URLs of your website a bit more "pretty" and SEO-friendly.
When I started implementing mod_rewrite in websites I had a problem in PHP as how to make a SEO friendly URL. All tutorials were geared towards how to implement mod_rewrite, about modifying .htaccess files, but none treated how to make the urls friendly with dynamic content.
He shares a function that he found that helped him a great deal - a method called friendlyURL. It changes a bit of text into a more friendly version of itself ("this is a test" becomes "this-is-a-test") that can be used in anything you'd want. An example could be in automatically generating links to other pages on your site that search engines can easily follow.