A free app for Android, by GeorgieLabs.

Music VU Visualizer Widgets is a free widget app for Android devices. It allows you to visualize your music using a spectrum and wave display. The widget includes the ability to mix multiple visualizers, change the background color, add your own background, and even place it on your home screen. It can be used with any music player, including those in the Android system.

Each segmented meter has a high-resolution first-meter segment and traditional digital styling. Specialty waveform displays and spectrum analyzers also offer you new and interesting ways to visualize your music. 

The app allows you to add multiple visualizers at the same time. It also allows you to add a background color to the widget.