What you should do next depends upon your personal goals. Do you want to increase the chances of getting a job? Do you want to learn new ways of analyzing problems? Do you want to start writing device drivers and operating system hacks? Any of the above could suggest a radically different answer.

If you're looking for employability, Java is pretty tough to beat. It will also help to demystify why many people claim that OO is "bolted on the side" of Perl.

Ruby is great if you want a pure OO language. If you really get daring, though, you could try Smalltalk or Squeek.

To really wrench your programming brain and look at things in a new light, I would strongly recommend checking out a logical (Prolog) or functional (Haskell, Lisp) language. Logical languages allow you to specify facts and rules and can infer answers for you. Functional languages allow you to provide function definitions and incrementally extend the language in a way that you won't see in an OO or procedural world. (it can also be bizarre to see a variable declared after it's used)

I could go on for a long time, but you get the idea. Where you go depends upon what you want. Good luck!

Cheers,
Ovid

New address of my CGI Course.
Silence is Evil (feel free to copy and distribute widely - note copyright text)