iTunes visualizers are closest most folks will ever come to experiencing synesthesia (with or) without pharmacological assistance. And, whether you are putting on a party or just want to kick back and enjoy some eye candy, iTunes and SoundSpectrum’s excellent G-Force and Aeon visualizers turn whatever you are listening to include a vibrant, moving collage of imagery.

G-Force 4.4 (version history, download) offers fixes and enhancements, including new ColorMaps, critical installer fixes, RealPlayer 15 support, enhanced Winamp support, and 64-bit support for Windows Media Player, Windows Media Center, the Screen Saver, and Standalone for Windows.

Developer Andy O’Meara teases G-Force 5, but doesn’t offer any clue on when that might arrive.

Synesthesia (Wikipedia) — From the ancient Greek σύν (syn), “together,” and αἴσθησις (aisthēsis), “sensation,” is a neurological condition in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway.
— Examples include seeing music, tasting color, etc.

SoundSpectrum also recently released Aeon 3.0 (version history, download), which includes 16 all-new Scenes and enhancements to many others, as well as new Themes and Categories with extended visual preference customization. Also look for installer fixes, RealPlayer 15 support, enhanced Winamp support, many GUI enhancements, and 64-bit support for Windows Media Player, Windows Media Center, and the Screen Saver for Windows.

The free versions of G-Force and Aeon deliver basic iTunes visualization with limited customization. Gold ($20) and Platinum ($30) versions deliver additional themes, preferences, customization and, in the case of the latter, stand-alone visualizer apps and screensavers for multiple platforms.

Related posts:
— Songs used by Apple: A big list and a few friends
— YouTube to MP3: How to download and convert music from YouTube
— Pandora desktop apps for Mac
— Mac Audio: Boom 1.5.1 clears up ML, sound issues
— Mission Log: A Roddenberry Star Trek Podcast