The 'World Defence Almanac' is an annual publication by Military Technology Magazine containing an up to date overview of all the world's defence forces. It covers areas such as the basic statistics of a country, the political and military setup and the key personnel, the organization of the military and paramilitary forces, the equipment used and all comments regarding defence reviews and arms purchase programs.
On top of covering all the world's countries and their armed forces, the Almanac also has a selection of articles covering some pertinent issues of the year, as well as an excellent editorial by long time editor Ezio Bonsignore.
In contrast to something like The Armed Forces of the European Union 2012-2013
there is a wealth of pictures, covering both the people, as well as important equipment for each country covered and the information is really up to date - i.e. the 2012 edition was published in January 2012 and actually includes the updates the year brought.
The only potential downside for those looking for a pure book on the subject is the advertising contained therein but then again getting all the information contained therein without advertising revenue for such a reasonable price is probably otherwise impossible.
If you are professionally or personally interested in defence matters, I would certainly recommend making this an annual purchase - the well organized and up to date overview is second to none and will keep you abreast of all the relevant developments in the world's armed forces.