Several states have joined together to file suit against the federal government challenging the constitutionality of the health care bill. Virginia has already passed a bill "that says neither the federal or state government can force residents to purchase health insurance."
One issue is the requirement in the bill which forces individuals to buy insurance under the threat of fine. The argument against this provision is pretty simple. Under the U.S. Constitution, the enumerated powers do not authorize the federal government to require anyone to purchase anything. The counterargument is that the commerce clause allows the federal government to regulate. However, if you choose not to purchase health insurance, then by definition, you are choosing not to engage in commerce. How can the government regulate commerce that does not exist? (Of course, that is not the only argument. In theory, I believe virtually every provision in the bill is unconstitutional, but my understanding is that this is one of the key arguments in the suit.)
I urge you to contact your local state representatives and governor and encourage them to support these lawsuits. If you are in a state that has filed, write them anyway expressing your support. I use www.congress.org to write emails to both state and federal representatives. It is easy (if you know your zip code) and free.