Just finished the book Game Change: Obama and the Clintons, McCain and Palin, and the Race of a Lifetime by John Heilemann and Mark Halperin. It's about the 2008 U.S. presidential race. Both Heliemann and Halperin have extensive inside knowledge about the campaigns and. apparently, have many inside sources.
Their information seems factual to me, with only a very small amount of supposition/conjecture. Of course, you'll need to read the book yourself to determine how much you believe.
What I can say is that it's a very entertaining, very informative inside look at political campaigns, how they work, what they involve and how they're managed.
While it doesn't reveal any huge surprises (who doesn't already know that McCain has a temper, Biden is prone to gaffes, Palin's stupid, Hillary is controlling excpet when it comes to Bill and Obama is a little green) it does provide a surprising amount of anecdotal evidence to support the preconceptions and manages to portray all of the involved parties as having many flaws while simultaneously making the reader sympathise with their plight/the pressures (and yes, I'm even including Palin...at times!).