[lionsong]

some fruits of my recent googling -

http://www.cacr.math.uwaterloo.ca/hac/ - a free handbook on cryptography, seems to be very thorough and working from the ground up

http://www.ciphersbyritter.com/LEARNING.HTM - a nice overview of general cryptographic concepts

http://www.techotopia.com/index.php/...%2B_Essentials - another generalised account of IT security concepts

a whole slew of cryptography notes, very interesting!
http://machacking.net/kb/files/Algor...Complexity.pdf
http://machacking.net/kb/files/dimacs.pdf
http://mathforum.org/library/topics/cryptography/ - DEEP

some nice bits on socket and pcap programming
http://www.tcpdump.org/pcap.htm
http://yuba.stanford.edu/~casado/pcap/section1.html
http://machacking.net/kb/files/sockinc.txt

http://machacking.net/kb/files/wp-over-pentest.pdf - a nice laymens treatment of pen-testing methods

this guy is such a G, check everything he writes but in the spirit of this post these two are gold
http://beej.us/guide/bgnet/
http://beej.us/guide/bgipc/

everyone loves cheatsheets, and gdb is a profoundly powerful tool
http://www.givemefish.com/ArticlesAn...tSheet_gdb.php
http://www.digilife.be/quickreferenc...0Reference.pdf

some great code auditing guides
http://www.metasploit.com/users/puss...pers/Audit.pdf
http://mixter.void.ru/vulns.html

and lastly this list seems mostly linux based but there are some promising looking links none the less
http://www.vanheusden.com/Linux/audit.html