The CakePHP MongoDB plugin. Include the plugin, create a model, flag it to be sent to Mongo, and boom, your'e in business. Simple, elegant.
Useful intro to using MongoDB with CakePHP. Works quite nicely, load the plugin, specify your model should use Mongo, and boom, you're in business.
An API framework for CakePHP. They've implemented the Twitter API, and a handful of others. Very cakey, fits into the whole CakePHP approach very well. Not sure if it'll actually be that useful or not.
A groupon clone site from Agriya, an Indian software company. No pricing information readily available online. Featured in the New York Times apparently, hap tip Glyn. Built on CakePHP.