Promising to combine old-school pitch shifting with plugin convenience, Pitchproof is a new free VST plugin from Aegean Music.
The plugin also serves as a harmoniser, and features a Blend control that enables you to adjust the wet and dry signal levels, a Pitch menu for setting harmonies by semitone, the ability to select the key you're working in and a Detune knob,
Pitchproof has a guitar tuner, too; it's actually inspired by guitar harmoniser pedals, but can also be used with other instruments.
You can download Pitchproof for free (in 32- and 64-bit Windows VST formats) from the Aegean Music website.