The Google Authenticator app is a great way to do just that, and the idea is simple. The app gives you a rotating security code that you need to enter whenever you sign in to your Google account from a new device. This means that even if someone cracks your password, they can't get into your account unless they have stolen whatever mobile device you have Authenticator on (of course, if someone steals your mobile device, you probably should shut down the device remotely and change all your accounts anyway).
If you've been using Google Authenticator, you know this already, and you also know that the app has been using the outdated dark Holo theme for far far too long. Now, more than one year from the Android 5.0 (and Material design) official release, Authenticator has gotten a UI update. Additionally, Android Wear is now supported, so you can get the security code on your smartwatch. Lastly, developers can start playing around with support for physical NFC keys.
download: Google Authenticator
source: Android Police