One very handy element in the Polymer ecosystem is the
core-pages tag. It's a very simple element (it just toggles sections of content on and off for you) but it's really useful for putting together single page apps.
core-pages is best used on simple applications, and can be really nice when combined with a menu and router using data-binding. I'll be diving into routers in the next couple of episodes of Polycasts so be sure to subscribe to the Google Developers channel if you want to receive updates when new episodes roll out.