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.
UVI Falcon - Sampler/synth hybrid instrument
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.
Pianoteq - Pianoteq is a virtual piano that runs on your computer.