Google I/O App Source Code on GitHub: Material Design, Android L, and More
If you're still curious about what Android L is all about - you know, what Material Design is, all that stuff - you can just take a look at Google's app from I/O 2014, which has been updated to include Material Design and the Android L Developer Preview. It's all available on GitHub, so you can dig around the source code to get an idea of how all the new stuff works, or just as a starting point. Take a look:
(Source: Google I/O Android App on GitHub)
You'll notice from the photo that the I/O app also includes Android Wear integration - that was a pretty big topic at I/O 2014, too. Keep in mind that you will need the Android L Preview system image to run this, but otherwise, it looks like a nice collection of resources.
The GitHub page spells out all the features of the app, but probably you're not too interested in that. More relevant is the collection of how-to resources to help you start messing around with the source code:
Check out the GitHub page for all the details, and see what's new in Android L.