GSnap - With GSnap you can get an auto-tune effect.
UVI Falcon - Sampler/synth hybrid instrument
Revoice Pro - Revoice Pro is an audio plugin used for vocal tuning, time correction and ADR.
Pianoteq - Pianoteq is a virtual piano that runs on your computer.
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.