Reddit reviews Unconventional Wisdom: Facts and Myths About American Voters

Actually by and large swing voters do not exist. If you want to find out a little bit more about how people vote I suggest Unconventional Wisdom: Facts and Myths about American Voters. They have a chapter devoted to swing voting. A very basic explanation is that the media over hypes swing voters, thus many people believe that there is this mysterious group of people that vote on a whim. It's largely not true. People vote mostly vote along party lines.

http://www.amazon.com/The-American-Campaign-Presidential-Campaigns/dp/1585446289 (this will supplement your textbook)

http://www.amazon.com/The-Imperfect-Primary-Controversies-Representation/dp/0415995779/ref=pd_sim_b_6 (Most recent, and pretty dang good)

http://www.amazon.com/Presidential-Primaries-Dynamics-Public-Choice/dp/0691022836 (Still a classic despite the age)

http://www.amazon.com/Unconventional-Wisdom-Facts-American-Voters/dp/0195366832 (not specific to presidential elections)

http://www.psqonline.org/APSBooks.cfm?idbook=12121 (Selections of articles concerning the last few elections)

http://www.press.umich.edu/titleDetailDesc.do?id=22213 (Best work on presidential third parties that exists)