We featured Audio Glow when it launched in November of last year. This ultra-stylish music visualizer takes the basic visual component of classic hi-fi systems and gives it a fresh coat of paint. It's gained quite a following thanks to eye-popping visuals and a huge degree of customization. Today's version 2.0 update adds some interesting options, most notably the new "Glowing Strings" visualization, below.
This nifty option is available as a $1 in-app purchase for the main Music Visualizer app, but the developer has kindly included a 5-minute preview that you can check out before buying.