HTML::Template does exactly what I need. It allows me to seperate the presentation from my code and isn't at all complex. It has a simple syntax with easy to understand documentation and examples. It gives you just enough of what you need without so much that you'd need a book to learn it thoroughly. There are also HTML::Template extension PMs you can find on CPAN that will let you integrate some degree of code or evaluations and calculations in your templates (if you're into that sort of thing).
HTML::Template was perfect for pulling the presentation part of my existing complex and details project into its own layer without making any sacrifices or major changes in the code itself. I've looked at HTML::Mason and Template::Toolkit and would certainly consider them under different circumstances, but for my needs HTML::Template is *perfect*.