The following links are closely related to the Audio Unit work I've been doing:
DSP Dimension website
Stephan M. Bernsee's DSP Dimension contains a pitch shifting algorithm tutorial and code samples.
Hitsquad Musician Network
A large database of audio effects, software instruments and other audio related software and information.
Open Tuning website
The website of Open Tuning by Philippe Gruchet, software which allows you to explore unlimited different tunings for MIDI instruments.
You can also go back to the Audio Units page.