The best overview for beginners. Suitable for classrooms and educational use as well as general interest, in audio or Ebook form.
A bit too technical for most of us, but this history, written by Arpanet pioneers who were involved in the early developments is very valuable source material.
Michael and Ronda Hauben's excellent book on the history of Usenet
Gregory Gromov's eccentric and psychedelic site.
An excellent site at Leiden University
Janet Abbate's book is great for socio-economic analysis
Great book on Arpanet origins by Katie Hafner et al - debunks the theory that the Internet was built to survive a nuclear attack
Another early Internet history, written in 1995 by Peter Salus