The best audio visualizer is WhiteCap by SoundSpectrum.
I consider this piece of software a breakthrough in terms of its ability to translate audio into reactive geometrics. Excellent synchronization.
You can download a trail version for free. There are two paid versions: a $20 version called WhiteCap Gold, and a $30 version called WhiteCap Platinum. The Platinum version includes a WhiteCap screen saver and support for multiple media players.
Overall Rating: ***** (five stars)
This review was Reactual Independent Evaluation.