CGI scripts
If you have a web site with access to your own cgi bin you can find many well written free scripts on the Internet to provide you with powerful extensions to your web site. You still have to install them, however, and update them when new versions and bug-fixes become available. This is not for beginners.
Find counters, clocks and more complicated scripts such as aguestbook and a random image displayer at Matt's script archive
Find more cgi scripts