I just started reading a period book:
Reminiscences and Remembrances of Captain Gronow, formerly of the Grenadier Guards: Anecdotes of the Camp, the Court, and the Clubs, at the Close of the Last War with France.
Most of the book is about life in Britain during the war, but there's a lengthy section near the end that gives a firsthand account of several battles. One of the various editions available has a good account of Waterloo.
http://books.google.com/books?id=XRE...page&q&f=false