On the Zend Developer Zone there's a new article from Vikram Vaswani about what's becoming a more popular pairing of technologies in PHP applications - using MongoDB with PHP.
In this article, I'll introduce you to MongoDB, one of the new generation of schema-less database systems that is quickly gaining the attention of open source developers. Over the next few pages, I'll guide you through the process of getting started with MongoDB, showing you how to install it, set up a data store, connect to it and read and write data using PHP.
He shows you how to get your full environment set up - a local install of MongoDB and the PHP shared object to interface with it - as well as plenty of code examples to get you pointed in the right direction. He also shows a bit of how to use the Morph PHP library to interface with the database.