What's the best programming language for a hobbyist?

TLDR: There are so many programming languages and frameworks out there... and there is so little time :( Which one would you learn just for the fun of it?

I have some experience with a bit of Pascal, C++ and C# from highschool but not much (I was mainly learning algorithms and concentrating less on actually building software). During uni I did some Java and continued with C# (+XNA). In the meantime I played a bit with PHP. After I graduated I got a job as a PHP developer (PHP, Javascript, CSS, HTML).

Now, after 2 years of work, I realise I need something else. I want to learn a new programming language, or continue learning one I started in school, something that will compensate for the lack of algorithms in my work (building websites with PHP can be tedious sometimes). I want to learn it in my spare time and I want to be able to build something with it, a small application of some sort... not really important what, but I want to use those algorithms I learned several years ago.

This brings me to my question ... what should I learn? What is the best programming language for a hobbyist. The kind of programming you do on weekends just because it's cool, because it keeps your brain moving and because it's fun and rewarding. What's the programming language that puts a smile on your face? :-)

What's your hobby? If web development I'd look at Python, Ruby or JavaScript.

If systems type stuff then Python, Perl or C. If you wanna be a hobby kernel hacker then C.

If games, well. I don't know.

I know a lot of people are going to say Python, which I would normally agree with. In this case though, I would almost say that some kind of Lisp might be a good idea. The lack of a complex syntax means you can just get started hacking around, and it would definitely "keep your brain moving," as you say.

Some kind of Scheme would probably be best. Racket, especially, is supported cross-platform, has a nice little IDE, and has plenty of libraries and community support.

Another point to consider: Would you want to be able to easily show off what you created? Then you should likely do HTML5/CSS/JavaScript so you could put it on your phone. Who knows? Maybe you will come up with an app idea that's commercial and you'd be set.

Ruby - because it is a little bit different to what you already know - which would be the entertainment factor and also might change how you write code elsewhere.