I have written code in these languages, in order of experience:

- PHP, Javascript. Java, Python, Perl, C

I've been doing some random walks on the massive list of programming languages on Wikipedia and I've found a few interesting choices. Here is a small list:

- Cofeescript http://coffeescript.org/

- Fantom http://fantom.org/

- HaXe http://haxe.org/

- Neko http://nekovm.org/specs

- K http://en.wikipedia.org/wiki/K_%28programming_language%29

- Factor http://factorcode.org/

- Ragel http://www.complang.org/ragel/

I think learning a niche language will be fun, could give me a different perspective than the procedural and OO languages I've used so far and could prove to be a valuable and marketable skill in the future.

Which exotic programming language would you recommend?