ESection is a free program for calculating and displaying spectral and other related analyses of sections of a speech signal. It can be used to demonstrate the different spectral properties of elements of speech. It can also calculate an LPC spectrum, autocorrelation and cepstrum analyses, and can display the signal as a waveform or as a spectrogram. It automatically finds formant and fundamental frequency values. More information.
RTGRAM is a free program for displaying a real-time scrolling speech spectrogram on Windows computers. More information.