If you want a political classic, of course, you can't miss with "All the King's Men" by Robert Penn Warren. (It also falls into the category of "If you haven't read this yet, you really should someday.")
They also suggest more current political reading, like "Angler," Barton Gellman's biography of Dick Cheney, and of course candidate bios and writings like Barack Obama's "Audacity of Hope" and John McCain's "Faith of my Fathers." (Although, really, I would suggest, the time to have read these was several months ago....)
And of course they also point readers to Amazon's Election 2008 which will give you your fill (and then some) of red titles, blue titles, and (for the chronically undecided) purple titles.