Soundplant - Play sound files with the computer keyboard
Magic Music Visuals - Fully-customizable and highly responsive visuals for live and recorded audio & MIDI.
CasterSoundboard - A soundboard for hot-keying and playing back sounds. (For podcasting)
MilkDrop - 3D audio visualization plugin, compatible with WinAmp plugin API
JN Soundboard - An open-source hotkey soundboard program
Kauna - Kauna is a music visualizer. Kauna renders any sound reproduction in system.