Here are two tools that can help you generate the art and make it look more professional:
- Official Google Device Art Generator - which generates the art for Nexus Devices
- 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!