I would also recommend Prolog. Logic programming takes a very different approach to programming problems, and it's helpful to understand how you solve problems in that kind of a framework even if you don't wind up using it for your day job. Problems which are easy to solve using Prolog are generally difficult (or cumbersome at best) to solve using imperative languages.

And you can start with AI::Prolog, an Prolog interpreter written in Perl. As for books about Prolog, I'd recommend the classic "Art of Prolog".