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.
Clownfish Voice Changer - Clownfish Voice Changer is multiple voice changing software for various chatting and gaming platforms.
Celemony Melodyne - Celemony Melodyne is the perfect quick and easy tool for all your tuning needs.
TalentedHack - A Pitch Correction LV2 plugin derived from Autotalent