Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
Magic Music Visuals - Fully-customizable and highly responsive visuals for live and recorded audio & MIDI.
FL Studio - Image-Line's FL Studio, now on it's 12th version, is a well-known music production suite and the most popular beat processor on the market, due no doubt to its longevity. Read more about FL Studio.
MilkDrop - 3D audio visualization plugin, compatible with WinAmp plugin API
Reaper - Reaper is a focused digital audio workstation (DAW) developed by Cockos. In the creation of the software, the digital audio technology company intended to make audio editing accessible to the masses.
Kauna - Kauna is a music visualizer. Kauna renders any sound reproduction in system.