Play comes with a set of sample applications in the the samples-and-test directory of the framework installation path. We use them to run our automated test suite, and you can take a look at them to discover typical play usages.
Yet Another Blog Engine
The final application from the play guide tutorial.
A simple forum application using JPA.
A full faetured job board application that uses the CRUD module to automatically generate the administration area.
An HTTP based chat application. We use the asynchronous request model to be able to handle a lot of simultaneous connected users without resources waste.
Based on the default GWT tutorial, it shows how to use GWT within a play application.
A clone of the the well known 37Signals TadaList application built using the Google App Engine support. It uses Siena as persistence engine.