I'm barely into Carl von Clausewitz' seminal work 'On War' and already I am fascinated.
Incidentally, I was originally made aware of his work via Borepatch's link (via Isegoria) to THIS.
Thus far, it's an interesting departure from Sun Tzu's 'The Art of War,' which is much more a practical guide, with specific strategies and tactics. Granted, there is a LOT left of the book itself, which was a labor of more than half of von Clauswitz' life (he died of cholera at 53, having joined the military at age 12). However, where Sun Tzu can be read as a handbook on the practical application of War, 'On War' is a collection of wisdom regarding the theory of War itself; it's causes, limitations, and factors. Although I have finished a mere 30ish pages of it, its application to a wider range of subjects is already apparent. The civilization we live in would be much better served, in my opinion, if more people were exposed to Clausewitz and less to Machiavelli.
So far, strongly recommended.