Google's Trends tool is an interesting way to gain a bird-eye perspective on the upcoming 2008 Presidential candidates. "Trends" shows an approximation of search volume for any given search term as compared to another. In the case of presidential candidates, you can see how much each candidate is being searched for on Google in comparison with other candidates.
For example, let's look at a few of the Republican candidates, in no particular order. Only four candidates are shown here for simplicity sake, and Hillary Clinton is included for reference.

The above graph shows search volume for each presidential candidate's name in the first row, and how many times those names are being referenced in the news (or, what Google considers to be "the news") in the second. Although this data should not be considered concrete real world data, you can still draw some interesting conclusions.
One of the more interesting candidates to watch has been Ron Paul, who has surged in search volume with almost no accompanying news coverage. This is probably due to the fact that Ron Paul does very well with social websites such as Digg, Slashdot, Reddit, etc. but not as well with the general media. It is interesting to note that each Republican candidate started out with mediocre search volume at the beginning of the year, but candidates like Ron Paul and Fred Thompson have surged recently.
Here is a chart of the Democratic candidates, again in no particular order. Ron Paul is included here for comparison purposes so you can easily reference between the two charts.

Opposite to the Republican graph, leading Democratic candidates like Hillary Clinton and Barack Obama peaked at the beginning of the year and have since fallen.
The data can be further broken down by region for even more interesting information.

We can see here that people in Washington D.C. search more for Hillary Clinton, while people in Illinois search for Barack Obama more.
Further comparisons can be made by pitting the two political parties directly against eachother in Google Trends. Here we compare Clinton, Obama, Paul, and Thompson - the four candidate who have shown the most movement in search volume throughout the year.

Here is a breakdown of the above graph by city:

Here we see that the popular search goes to Paul in Austin, TX and to Obama in Chicago, IL. Compare this to the election results from 2004:

Perhaps it should already be obvious, but both data sources show Texas being heavily Republican while Illinois is heavily Democrat. This just goes to show the extent to which search volume trends correlate to real world election results. Again, none of the information should be taken as concrete because there are several reasons why search data could skew one way or the other, but the data is interesting nonetheless.
For comparison, here is a record of searches performed before the 2004 election for George Bush and John Kerry.

The overall closeness of the search volume for each candidate seemed to predict accurately the closeness of the final vote. Unfortunately data is not available for the 2000 election. It would be interesting to see how far apart search volume is in a race that wasn't quite as close.
There are many conclusions you can draw from this data, but the most important is that the election in 2008 could still go to anybody. It will certainly be interesting to watch how search volume correlates to real world election results.
Resources:
Google Trends Republican Candidates
Google Trends Democrat Candidates
Google Trends Republicans vs. Democrats
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