From the November 2008 Idaho Observer:
How did third party candidates do in the Nov. 4 general election?
Qualified answers to the question above were hard to find and they were not very well reported in the two-party media this time around. But, as we suspected, a respectable percentage of the electorate voted third party in 2008 due to the growing numbers of voters who have become disenchanted with both blue donkeys and red elephants.
By The Idaho Observer
The official tally for the 2008 election shows that Ralph Nader, who ran as an independent, received the most votes—697,251 and Alan Keyes of the Independent Party received the least amount of votes—41,241.
Other third party candidates received the following number of votes:
Bob Barr—510,570
(Libertarian Party)
Chuck Baldwin—181,796
(Constitution Party)
Cynthia McKinney—152,292
(Green Party)
The total tally for the five "frontrunner" third party candidates was 1,583,150. The combined total votes cast for omniparty candidates Obama and McCain were 125, 225,901. So third party candidates netted nearly eight percent of the popular vote (if you have faith in modern vote tallies).
Although there are two other registered parties that ran presidential candidates in 2008 (Charles Jay, Boston Tea Party, and Brian Moore, Socialist Party), they were not on the ballot in many states and it was difficult to find a total count nationally for these candidates.
It is believed that Ron Paul and Hillary Clinton received the majority of "write in" votes. However, we may never know how many votes they received. Many states don’t tally any write-in votes for president until December and sometimes January. Certain areas of the country (illegally) don’t count them at all. Washington, Oregon, Alaska, and the District of Columbia all refuse to provide a tally for even legally filed and declared write-in candidates.
In the case of the District of Columbia, this is especially egregious, since a D.C. court explicitly ordered such tallies for declared write-in presidential candidates in 1975 in the aftermath of the Kamins v D.C. Board of Elections lawsuit.
Also, in the case of Oregon, the State Supreme Court ruled in 1945 that the Oregon Constitution protects write-in votes.
New York city habitually fails to count any write-in votes for the declared write-in presidential candidates. The elections board says it is too much work to take down the heavy rolls of paper from the mechanical voting machines and look at them.
About 15 counties in Pennsylvania, including Philadelphia, also regularly fail to tally any write-in votes at general elections. A proposed lawsuit to challenge this behavior in Pennsylvania has been talked about for almost two years now, but no attorneys have filed a lawsuit to date.