Online the Napoleon Series website is one of the most scholarly resources out there. Simply masses of information about armies, generals, battles, campaigns, tactics, organsations, uniforms, regiment histories...
http://www.napoleon-series.org/
One of the best general histories of the Waterloo campaign I've read in recent years is Peter Hofschroer's 2-work series:
http://www.amazon.co.uk/1815-Waterloo-C ... 180&sr=1-6
http://www.amazon.co.uk/1815-Waterloo-C ... 80&sr=1-11
Hofschroer writes from a German perspective and his main point is to correct the subordinate role that British and other English-speaking historians have given the Prussian army and other German troops in the campaign. He has axes to grind and his narrative gets a little slanted especially when being critical of the delayed response of the Duke of Wellington to the news of the initial French crossing of the Belgian border, but on the whole these are excellent books giving a lot of tactical and regimental detail of the combat without getting bogged down.
One of the things his account of the opening moves of the campaign highlights is how similar it feels to the strategic moves of ACW armies, nothing really has changed between the two other than some minor benefits from railroads the Union had and the incessant interference by telegraph messages from Washington that Hooker and then Meade had to deal with! But on the ground, the considerations of moving battalions, batteries, squadrons, divisions and corps is the same and in some ways the "last chance" offensive by Napoleon in 1815, north into Belgium, mirrors somewhat the Gettysburg campaign. Napoleon was facing a stronger army and had to win a quick decisive victory or else the war would be lost.