Speedster is an Audio Units effect plugin that pitch shifts and time-stretches in real-time. A clever algorithm allows for controlling (and automating!) pitch and speed independently.
As a powerful addition it can also perform stereo/center separation, so that the user has independent control not only of the right and left side of the signal, but also of the center.
Speedster is a freeware plugin, due for release later in April 2004, a preview version is already available for download.