You really have about three decent choices here:
1) PHP, 2) Ruby & Rails, 3) Python & Django
Of these three, I believe that PHP really is the best choice. While you could learn either of the other two technologies, you can find a number of books just on 'PHP and MySQL' and a heap of online documentation on the same. Additionally, there are hundreds of 3rd party modules and programs written PHP you can either integrate directly into your site or use to learn from. PHP will scale better than Ruby on Rails and is just as easy (some would say easier) to work with. It will have a much shorter learning curve than any of the Python frameworks and is also more forgiving of programming mistakes.
Beyond those three, several exotic choices exist such as Smalltalk/Seaside or PLT Scheme. However, documentation and third party modules won't be as readily available.
Of these three, I believe that PHP really is the best choice. While you could learn either of the other two technologies, you can find a number of books just on 'PHP and MySQL' and a heap of online documentation on the same. Additionally, there are hundreds of 3rd party modules and programs written PHP you can either integrate directly into your site or use to learn from. PHP will scale better than Ruby on Rails and is just as easy (some would say easier) to work with. It will have a much shorter learning curve than any of the Python frameworks and is also more forgiving of programming mistakes.
Beyond those three, several exotic choices exist such as Smalltalk/Seaside or PLT Scheme. However, documentation and third party modules won't be as readily available.