If you need to generate some nice promotional pictures, it's good sometimes to put them into context of a real device. You can of course take a picture of your phone or tablet with your game, but I bet it won't look good enough.

Here are two tools that can help you generate the art and make it look more professional:

1. Official Google Device Art Generator - which generates the art for Nexus Devices
2. Android Asset Studio - free tool that offers few more devices

Android Asset Studio can do more. It can generate the sets of icons and other assets for different screen sizes and densities. This is based on the same generator in Android Development Tools - you can see it when creating a new project in Eclipse.

Other tools  include nine-patch generator, notification icon generator and more. Explore the options yourself and bookmark the tools, they are definitely useful!

If you generate some nice art for your game, post the picture in the comments!