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.
Revoice Pro - Revoice Pro is an audio plugin used for vocal tuning, time correction and ADR.
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.