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
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
Huge list of Pd Objects
Miller Puckette recounts the history of Max and music patchers after 17 years
Wiki page on Max with information about Pd