Sic Semper notes a couple of secession movements within the US:
Texan and
Californian independence from the US, and then
they noted the
East Washington State secession movement that is starting. And now Michelle Malkin notes secessionism among
native Hawaiians.
This led to several other secessionst links, like
American Secession Project, an attempt at an umbrella organization for such groups within the US, as
Secession.net seeks to do worldwide.
Most often when I have met people who seriously advocate secessionism outside of the context of ethnic nationalism, it has been an essentially immature mindset in action. Secessionism is a cool idea if you don't need to worry about consequences. Even here in Northern Virginia, I hear rumbles of secession occasionally - then again, whom in Virginia hasn't heard about their own piece of the patchwork thinking it could do better without Richmond? But rather than slogging through the hard path of activism and making their government more responsive to their needs by raising their voices, they look to the easy, lazy path and say "let's just not answer to them anymore. Then we don't need to argue our case."
There are serious places in the globe where secession is considered by serious men for serious reasons. None of them is in the United States in 2005.