Template Toolkit
I am officially a huge fan of the Template Toolkit module for perl. I’ve been developing an online survey application recently using the TT stuff along with the CGI::Application module, and it has made writing a medium sized perl web application astoundingly easy. I’ve been able to spend hugely more of my time writing actual application logic rather than stupid infrastructure code, and the infrastructure has held up easily as the application has grown from a few hundred lines of code to several thousand. It manages this trick without all of the overhead entailed by using something like Java Struts, which is great for large applications but overkill for medium sized stuff. And the templates written with the TT language are vastly more enjoyable to deal with than jsp (which I like less the more I use it).