Flossmanuals has online manuals for Ardour, Audacity, Chuck, Csound, Fluxus, and Pure Data.
Musica/Tecnologia's latest issue is dedicated to the phase vocoder.
An International Archive of Sound Art.
The Montréal Sound Map.
Sound and wave animations from Music Science at UNSW.
The Musical Acoustics Research Library (MARL) contains digitised archive documents in musical acoustics. There are early papers and correspondence by James Beauchamp, Max Mathews, and Jean-Claude Risset, e.g. some documents pertaining to Rissets research on trumpet tones.