sndpeek is just what it sounds (and looks) like:

• real-time 3D animated display/playback
• can use mic-input or wav/aiff/snd/raw/mat file (with playback)
• time-domain waveform
• FFT magnitude spectrum
• 3D waterfall plot
• lissajous! (interchannel correlation)
• rotatable and scalable display
• freeze frame! (for didactic purposes)
• real-time spectral feature extraction (centroid, rms, flux, rolloff)
• available on MacOS X, Linux, and Windows under GPL
• part of the sndtools distribution.

Original homepage: http://soundlab.cs.princeton.edu/software/sndpeek/