I have done some consulting for a company (which shall remain nameless) whose primary product is a cross-platform systems monitoring tool which includes automated performance tuning and optimization. It is written in Perl.

The product is quite robust and highly customizable, taking advantage of the ability that Perl confers to quickly implement customized tools on a variety of platforms.

And it's done well through the downturn.

Mention should also be made of all the web sites which are built with Perl. Are those not commercial products?