It's not always necesary to reinvent the wheel, chances are somebody already developed a script or application that supports the features you want to add on your website. The following repositories literally hold thousands of free and cheap priced scripts.

Hot Scripts
The net's largest PHP, CGI, Perl, JavaScript and ASP script collection and resource web portal.

The CGI Resource Index
Thousands of CGI scripts writtwn in Perl and other language.

The ASP Resource Index
Guide for ASP web applications, scripts and other related resources for Active Server Pages.