Business Directory

I need someone who is familiar with developing in modular setups... I need to have a framework that will allow progression, scalability, and the ability to add new modules and functionality that can be linked to each other module. The first module is a business directory, with various sorting and filtering features. I would like to focus on this module first. The searching and filtering system should be similar to this: <[login to view URL]> with a few extra features and filtering options etc... PHP, MYSQL & AJAX a must.