I am in the process of architecting a new web site. I am planning on using HTML/Javascript/Ajax on the client side, and MySQL. The question is what would be the best choice of technology on the server side to provide a scalable (within reason) solution.

I don't want to go down the full-fat J2EE route if at all possible. What I would like to build is a simple server farm. Are there easy to use frameworks in PHP that would make this possible? How would this work with Apache and can these it be used to act as a load balancer?

I would also consider Java (J2SE) on the server side as it should be a more robust and performant solution. For either option I would be looking to use free tools....

All architectural advice, or info on good references would be appreciated as I am finding it difficult navigating the line between small hobbyist website and full-on enterprise level architectures.