From CCRMA Wiki
Floss Manual - Excellent Resource
This free manual has excellent tutorials and great lists of PD objects organized by function - math, audio, glue, etc.
Programming Electronic Music in Pd
This is another great resource with lots of examples.
Pages where people have posted interesting projects
Official Pd Documentation http://msp.ucsd.edu/Pd_documentation/
Freesound This isn't a Pd source per se but it is an invaluable resource. Create a free account and you can get all sorts of sound material for your patches. http://freesound.org
Pd for Max Users http://puredata.info/docs/tutorials/PdForMaxUsers
Huge list of Pd Objects" http://protman.com/content/list-puredata-objects-and-extended-objects
Miller Puckette recounts the history of Max and music patchers after 17 years http://msp.ucsd.edu/Publications/dartmouth-reprint.dir/
Wiki page on Max with information about Pd http://en.wikipedia.org/wiki/Max_(software)