Here is a cool program I found to help with vocal practice, Tartini.

Tartini is a program designed as a practical music analysis tool for singers and instrumentalists.
Just plug in a microphone and instantly your computer will give real-time feedback including:-

* Accurate pitch contours for visualising intonation, vibrato shape, tuning or just which note is being played
* Loudness graphs, to help analyse dynamics
* Harmonic structure of a note describing timbre

The program is named after the violinist and composer Giuseppe Tartini. In 1714, he discovered that if two related notes were played simultaneously on a violin, a third sound could be heard. The frequency of the third sound is the difference in frequencies of the two original notes. Tartini taught his students that unless they could hear the third sound, they were playing out of tune. Thus we see him as an early example of someone trying to apply scientific principles to understanding and improving musical technique.