Apache: The Apache Web server, used on a majority of Web sites, is freely available from http://www.apache.org/ in source format. Documentation for Apache, as well as tutorials on how to use and administer it, can be found at that Web site, and also at http://www.apacheweek.com/, a weekly newsletter for Apache users.
mod_perl: The mod_perl home page is at http://perl.apache.org/ and has pointers to tutorials and utilities describing how to use it well.
MySQL: The MySQL home page is http://www.mysql.com/, although there are numerous mirrors around the world. Some additional MySQL documentation can be found at http://www.turbolift.com/.
Embperl: Embperl now has its own web site at http://perl.apache.org/embperl/.
Database-Backed Web Sites, a book by Phil Greenspun on the creation and maintenance of databases and web sites, is a classic that should be read by anyone using these tools. See http://photo.net/wtr/ for a full copy of the book (as well as a draft of the coming sequel), along with many other useful tidbits.
All listings referred to in this article are available by anonymous download in the file ftp://ftp.ssc.com/pub/lj/listings/issue56/3137.tgz.