I feel like I've been telling a lot of people this lately, but the best answer to "what should I learn" is almost always "to be a better programmer." Most of the skills that make a good programmer are not language dependent, and even good styles of programming for specific types of languages (OO vs. functional) are exportable across their families. Just about everything you'll learn in Perl Best Practices applies to Java, C, PHP, and the flavor of the month five years from now.

So first and foremost, learn to be a better programmer. You will then find yourself in the position to quickly be able to pick up the basics of a new language, and just as quickly work your way through whatever special topics you need to address. In an industry where just about all of the specifics that you know right now will be obsolete by the end of the year (whether you know it or not), that sort of flexibility and confidence grounded in ability to say "yes I can" is the most important skill to have.

Cheers!