GSnap - With GSnap you can get an auto-tune effect.
UVI Falcon - Sampler/synth hybrid instrument
Celemony Melodyne - Celemony Melodyne is the perfect quick and easy tool for all your tuning needs.
Pianoteq - Pianoteq is a virtual piano that runs on your computer.
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.
LinuxSampler - LinuxSampler - free, open source pure software audio sampler with professional grade features.