Amendment X. Reserved Powers.In the Supreme Court, this amendment is cited mostly in dissents. This amendment is the linchpin for much of the tea party protests. There is a Tenth Amendment organization fighting to limit the power of the federal government based upon the Tenth Amendment.
The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people
Go here for a very interesting and entertaining speech on the need for states to exercise more power and stand up to the United States government, as Northern abolitionist states did in the fight against slavery.