The Pragmatic Programmer: After PHP, what's next?

Question

I'm reading The Pragmatic Programmer and I'm on the section where the authors suggest that we learn a new language every year. I'm currently a PHP developer and I'm wondering, what should I learn next?

I'm looking for a language that will help me improve my skills and help me with my daily tasks. Something useful.

Any suggestions?

[Edit] Awesome answers guys! Thanks. I'm still contemplating your answers and I'm leaning on studying Python or a functional prgoramming language as you guys have suggested (maybe Lisp).

Answer 1

Going for the option of learning something new, rather than something a bit like what you have done before.

C++ or C
A low level language that requires manual memory management and teaches you how things work at a lower level. Good community base and is one of the languages that a programmer should learn.

I would suggest one of these over assembly as although assembly is even lower level it is pain to produce a project. Learning a language like C or C++ will have the bonus of allowing you to learn assembly very fast if you ever want to do it, as there are relatively few new concepts compared to going from Java to assembly.

Haskell
A purely functional language that totally changes the way you look at some problems. It takes a lot of effort lean if you are already used to a imperative style of writing code.

It has the great advantage of teaching you the joys of recursion, and even if you are never payed to write a line of Haskell it should impact the code you write in other languages, allowing you to see better and cleaner solutions.

Java or C#
If you don't use PHP in an Object Oriented way (Not just using classes, but features like inheritance as well), then these languages force you to write in a OO style. I wouldn't recommend these if you are happy with OO programming.