GSnap - With GSnap you can get an auto-tune effect.
Voicemod - What are the voice changers? How do these work? Are these illegal? What is a soundboard? Find all the answers here. Voicemod - The Best FREE Voice Changer
Revoice Pro - Revoice Pro is an audio plugin used for vocal tuning, time correction and ADR.
CrispyTuner - Fully featured vocal tuning suite.
Clownfish Voice Changer - Clownfish Voice Changer is multiple voice changing software for various chatting and gaming platforms.
Antares Auto-Tune Pro - Auto-Tune Pro by Antares is the latest and enhanced version of Auto-Tune that offers Auto Mode to correct pitch and Graph Mode for step-by-step modifications of time and pitch.