Scribd is a great publishing site for PDFs and PPTs on a wide variety of topics. I have not visited the site lately, but it seems that the Scribd document repository has reached critical mass, and practically anything can be found there now. In fact, even too much. I have started to put of few documents there myself, and will later post a few of the interesting links I have found.
Shamir's Third Law and other Tales from the Crypt