One of my main areas of historical study and interest is the French Revolution, and more specifically, how international relations and politics were played out during the time period. While I am aware of the broader trends going on, such as continental suspicion and fear of what the Revolution would mean for other countries combined with the desire to see France brought low, I'm looking for anything that goes more in depth on the subject.
French Society in Revolution: 1789-1799 by David Andress is a more historical survey on society during the Revolution.
The Campaigns of Napoleon by David Chandler is the absolute tome of all tomes on the Napoleonic Wars. Good luck getting one; I picked up the last sub $100 recently as I wanted a hardcopy. There are two more used for $120 and everything after that is anywhere from $200-$350. It's freaking enormous though and a god amongst Napoleonic works.
Engineering the Revolution: Arms & Enlightenment in France, 1763-1815 by Ken Alder, which focuses on the technological, social, and political aspects of retooling the French military to better fight in the future, which is important for later dominance under Napoleon's rule.
The Bayonets of the Republic: Motivation and Tactics in the Army of Revolutionary France, 1791-94 by John A. Lynn is one of the best books about the Revolutionary armies and how they fought/were made up of.
Swords Around a Throne: Napoleon's Grand Armee by John Elting. As the book list describes it's not an operational history (e.g.: Chandler's work above) but a functional one; it breaks down every component from the Ancien Regime's army, the revolutionary army, and ultimately Napoleon's army. The cooks, the grenadiers, the hussars et. al are analyzed from the top down individually. Again, a freaking tome so prepare yourself.
The Origins of the Wars of German Unification by William Carr is a little handbook that is dense with information on, you guessed it, post-Napoleonic German nationalism and the wars that lead to unification. While tertiary to the topic at hand I do feel strongly, as do most academics for that matter, that the French Revolution and Napoleon in general are directly responsible for the events in this work and Carr discusses that in depth. If you want to see the legacy of the revolution in Germany this is the work to buy. Only ships from Europe I believe so prepare for those costs if that's right.