Google has this Device Art Generator tool (http://developer.android.com/distribute/promote/device-art.html) that allows you to drop the screen shot of your Android app onto one of three Nexus devices – Nexus 5, Nexus 7, and Nexus 10:
To use this Device Art Generator, first capture your screen shots of your app (such as using Eclipse). For example, I have captured the Home screen of my Note 3 as shown below:
Next, drag and drop it over one of the three devices and it will now generate a screenshot of your app with the selected device skin:
You can optionally apply a shadow and screen glare to the device image. You can also rotate the image.
Right-click on the image and save it to your local computer. You can now use it in your marketing materials!