2008 didn't really do anything for me. After the financial crisis, Obama had pretty much locked-up the election.
I'm too young to really recall 2000.
So, for me 2004 takes the cake. It was the first post-9/11 election, the candidates why no way "entertaining" were sometimes quite interesting. Like mentioned earlier, it was kind of the last "old-school" elections. The 2004 election, to me, just sums up all that America was at that time--a nation in transistion (Unraveling-->Crisis)
How is it the last "old school" election? Not really sure what you mean.
Between 2004 and 2008, the influence of social networking on elections increased 1,000-fold. In 2004, you didn't need a Facebook page to win. That cannot be said anymore. Hell, in 2004 barely anybody had heard of "blogging". Traditional news media played a much larger role in 2004. Now, traditional media (and thus big money) no longer controls the stream of information available to the voter.