Opponents of nullification usually cite VI.1.2 (the supremacy clause) of the Constitution to argue-away the idea of a State's authority to nullify federal law:
Article VI; Paragraph 2
This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the Contrary notwithstanding. [emphasis added]Those that oppose nullification would have us believe that VI.1.2 makes the federal government superior to the governments of the several States. That is NOT what VI.1.2 states. The above emphasized text makes it clear that only those laws made in Pursuance of the Constitution shall the supreme Law of the Land. Laws made in pursuance of the Constitution are those made under the authority delegated, by the States, to the federal government in Article I; Section 8. Laws not made in pursuance of the Constitution (like obamacare) are not law within the several States and neither the States, nor the People, are obligated to obey them.
See also: Amendment IX and Amendment X
Liberty begins at home, not in Washington. The protection of our liberty must be performed at home. There's much fanfare around federal elections, but the most important elections are those that seat your state and local representatives. By supporting candidates that will jealously guard your liberty you can stack your government with those that will resist federal usurpation.
Tom Woods is the 21st century poster boy for nullification. Well worth 25 minutes to hear what he has to say...
If you don't have 25 minutes right now, here's a 7 minute bit...
Tom Woods on Freedom Watch 07/03/10 p.2/5
The Tenth Amendment Center is a tremendous resource for information on nullification.