While it's not a complete example (it doesn't do any server-side communication, yet), I've been building a larger example app at http://bbclonemail.heroku.com
This project serves two purposes for me: providing a more in-depth example app, and providing a playground for new ideas that I have which often end up in my Backbone.Marionette add-on (go to http://github.com/derickbailey/backbone.marionette).
There are also several good examples listed in my http://backbonetraining.net/resources page, including a Wine Cellar application, a backbone 'store', and a handful of sample projects on github from various people.