I read:

Apart from the on-line documentation and help files, have there been any books published about PD?

http://www.crca.ucsd.edu/~msp/techniques/latest/book-html/

the max/msp manual/tutorials you can find online should also apply to a large extent, (http://www.cycling74.com/products/dldoc.html)

a couple of years ago I read Winkler's book (http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=4435) just because I snapped it up relatively cheap in england - but I was rather disappointed.

Then there are several classic texts on sythesis that are pretty good:

Roads, The Computer Music Tutorial (don't take this with you when travelling ;) Roads, Microsound (If you happen to be into granular synthesis) Dodge/Jerse, Computer Music (a rather compact review of computer music techniques) Moore, Elements of Computer Music (if you want to know what's going on behind the mirror, I found it excellent, but a little background in music and programming wont hurt)

regards,

x