I have a sneaking suspicion that we're going to be seeing a sharp increase in the already-astronomical number of books about various aspects of Abraham Lincoln's life over the next year or so as we approach the bicentennial of his birth. Authors will almost certainly continue to leave no Lincoln stone unturned (rail unsplit?) as they work over old ground and/or attempt to tread new paths.
Allen C. Guelzo's Lincoln and Douglas: The Debates that Defined America (Simon & Schuster) takes a narrow look at the seven debates waged between Lincoln and incumbent Stephan A. Douglas during the senatorial contest of 1858. Guelzo argues, quite fairly, that the debates were largely responsible for Lincoln's elevation onto the national stage which resulted in the delivery of his famous Cooper Union speech in early 1860 and allowed him to be seen as a serious contender for the Republican presidential nomination that year.
The book is focused, providing just barely enough background information on the issues, the run-up to the campaign and even the non-debate portion of the contest. Guelzo hones in on each debate with an examination of the setting, the various arguments made and the perceptions left by Lincoln and Douglas. It's a well-written and well-researched book with fine footnotes and a good historiographical wrap-up.