GSnap - With GSnap you can get an auto-tune effect.
Soundplant - Play sound files with the computer keyboard
Revoice Pro - Revoice Pro is an audio plugin used for vocal tuning, time correction and ADR.
CasterSoundboard - A soundboard for hot-keying and playing back sounds. (For podcasting)
Voxal - Modify your voice in any application that uses a microphone. From girl to alien, the voice options for online video games, avatars and podcasts are limitless.
JN Soundboard - An open-source hotkey soundboard program