.htaccess

useful rundown of .htaccess stuff. [...]

Ultimate htaccess Article

Thorough and useful bunch of tips on using your htaccess file. [...]

.htaccess editor

htaccess cheatsheet

this cheatsheet is pretty useful if you have access to your htaccess file. [...]

.htaccess tutorial

Tutorial on using and utilising the Apache .htaccess file. [...]

HTACCESS Wrappers With PHP

Another link from Simon Willison: HTACCESS Wrappers With PHP. [...]

Some neat .htaccess tips and tricks

...including:Redirect Visitors While You Update Your SiteHandle Moved or Renamed PagesCreate User Friendly URLs [...]

file extensions with php

you can drop the file extension in your url's to leave nice and clean addresses like theletter.co.uk/contact instead of theletter.co.uk/contact.php. [...]