A wonderful article on how to setup Client SSL authentication. Includes all the openssl commands and apache config variables.
Just what it says on the tin, very handy.
Interesting write up by James at Incsub on how they handle scale on edublogs. Some good advice although a little light on specifics, a good starting point for research.
Code snippet to protect .svn / .bzr / CVS directories within apache via the .htaccess file for a single site.
Code snippet to protect .svn / .bzr / CVS directories within apache system wide in the httpd.conf file.
A patch for mod_auth_mysql to support the new phpass format used in WordPress 2.5+. It's an apache mod.
ircmaxwell benchmarks Lighttpd versus Apache when serving static files. Results are overwhelmingly in favour of lighttpd.