On the DealTaker blog there's a recent post aiming to help you make the transition between a more traditional MySQL relational database structure over to one of the currently popular NoSQL databases MongoDB.
OK I'm going to assume you know what MongoDB is, so I'm not going to go over “what mongoDB is” or “what NoSQL is”. I'm going to do this series in a little different styling than my other tutorial series have been, so let just jump right in.
He links you to two resources, getting Mongo installed and the extension for PHP that you can use to connect your applications to it. After that, it's all code examples showing a side-by-side comparison of the MySQL version and the MongoDB version of everything from connecting to the database out to some more advanced queries.