Rumors are swirling around that Alan Keyes is preparing to make good on his threat to leave the Republican Party if they nominated someone who he felt was insufficiently zealous against abortion. His new party of choice is the Constitution Party,an openly theocratic party with ties to the militia movement. The party is already on the ballot in a dozen or so states, but would have to petition their way on to the rest.
The Constitution Party, formerly the U.S. Taxpayers Party, has been around since the early nineties when Howard Phillips tried to pull a bunch of far right parties together into a common front to support a Pat Buchanan presidential bid, should he bolt the Republicans as they expected. He didn't that year and the party put Phillips up as a candidate. Some other far right parties have talked merger and endorsed the party's candidate in the past, but they have not managed to expand their front any further.
One problem for the Constitution Party is that they have never managed to recruit a well-known name as a candidate. In 2004 they flirted with Roy Moore as a candidate. He was the Alabama judge who lost his job over his desire to plant a giant Ten Commandments monument in the lobby of the court house and defy the Supreme Court's order to remove it. Moore waffled too long and they ended up nominating Michael Peroutka, hardly a household name. Keyes would be the biggest name they have ever captured.
On the far left, Ralph Nader is running again. The Greens will no longer have him, so he is going it alone. Don't feel bad for the Greens, they are maintaining their quota of egotistical crackpots by gaining Mike Gravel. Gravel has jumped into Green Party politics by endorsing Jesse Johnson the nomination to head the Green Party ticket. The site Third Party Watch thinks Gravel's involvement is a sign that the Greens are becoming more mainstream. I think it shows the opposite, but I have a strong dislike for Gravel.
So far, the Republicans appear to have more to fear from third party erosion of their base that do the Democrats, but that could still change.