If you are willing to learn a MVC framework, I would recommend Python/Django and PyCharm. Rationale:
- Python is easy to pick up; it is closer to pseudocode than anything (don't be annoyed by the 'indentation as block delimiter' thing, after some time you will find it a great idea).
- Django has very nice ideas - the instant CRUD of Django admin is killer.
- PyCharm is not very expensive, has a 30 day full working trial and is cross-platform
The Django setup for Windows is a bit annoying because every tutorial seems to pretend you are running some Unix flavor; sometimes you have to use the command line, and Windows CLI support is half-baked (if you are on Windows, get a decent terminal and install some Windows native GNU tools). Don't be scared of command line, look for windows specific instructions and don't lose heart - setup is only once.
After setup, the learning curve is smooth, just follow along the Django tutorial. I assure you an enlightening experience that will change the way you program in other languages.
About the other dynamic languages:
- PHP: it is ubiquitous (even the cheapest hosting offers includes PHP support) and easy to get you started. If you want to learn something in order to improve your chance of getting a job, go for PHP. But will it make you a better programmer? I don't think so. As a language it is slowly evolving from a nice hack to a serious language, but still has a lot of dark corners (my pet peeve is how automatic typecasting is implemented).
- Ruby: it is very similar to Python, perhaps even more expressive (too much for my taste: like Perl, it encourages a very personal style and while I love Perl, I have a hard time understanding even my own scripts after a few weeks). IMHO, Python code is easier to maintain in the long term, specially when larger teams are involved. Rails is worth a try. I've flirted with Rails but ended up picking Django, perhaps you experience will be distinct.