I highly recommend the Encyclopedia of Human-Computer Interaction now being assembled by Mads Soegaard and the team at Interaction-Design.org. At the time I write this (July 2011) seven chapters are available, but I have examined the Table of Contents (not available to the public) and the breadth and depth of the invited contributions are quite impressive. The Contents I saw had 56 chapter covering an extremely wide range of topics, all with highly qualified authorities as authors.
The chapters now available cover the gamut from A to V (Action Research to Visual Representation). All are available free, available for downloading, reading on line, and even excerpting (don't forget to give proper credit and citation), all under a Creative Commons copyright agreement.
I won't write views of the chapters other than to say that I highly recommend them for professionals interested in learning about a new area of HCI and for educators interested in giving students excellent reference and educational material.
Caveat: I often show up in the citations. I have written a commentary for one chapter (Marc Hassensahl's excellent "User Experience and Experience Design") and I am in the process of writing a commentary for another chapter (which has not yet been released).
Citation: Soegaard, Mads, et al. (Eds). Encyclopedia of Human-Computer Interaction. http://www.interaction-design.org/encyclopedia/