So I'm trying to get into web development - once you've got past xHTML and CSS what you can do becomes pretty limited and you need to start playing around with server and client side scripting languages. The question for me is: which ones do I make the effort of learning?

I know how popular PHP is but I was wondering whether to consider any others - I'm not talking about which is the best one for beginners, just what do the different 'big-boys' do?

I'm talking about Perl, Ruby/Ruby on rails, Python etc - all these I hear about - what do they do individually? What makes them different from each other? What are the pros and cons of each?
Or maybe it's a mac/pc situation where its each developer to his own.

Any help would be greatly appreciated .