Revoice Pro - Revoice Pro is an audio plugin used for vocal tuning, time correction and ADR.
GSnap - With GSnap you can get an auto-tune effect.
Kontakt - With KONTAKT 6, you can sound like a snare drum, a symphony orchestra, or anything in between, from a universe of sampled instruments.
Celemony Melodyne - Celemony Melodyne is the perfect quick and easy tool for all your tuning needs.
LinuxSampler - LinuxSampler - free, open source pure software audio sampler with professional grade features.
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.