Professor Steven J. Willis (University of Florida College of Law) has filed an amicus curiae brief in support of the appellants in Thomas More Law Center v. Obama. The brief primarily addresses whether the minimum coverage requirement can be justified constitutionally as a tax. And it analyzes not so much whether 1501(b) exceeds the taxing power, but rather whether it is effectively prohibited by the Constitution because it is not a duty, impost, excise tax, or income tax -- the only forms of taxation (according to Professor Willis) authorized by the Constitution. You can access the brief here.
Professor Willis, along with co-author Nakku Chung, has written two interesting articles, both published in Tax Notes, that explore these issues in much greater depth: Of Constitutional Decapitation and Healthcare, 128 Tax Notes 169 (July 12, 2010), and Oy Yes, the Healthcare Penalty is Unconstitutional, 129 Tax Notes 725 (Nov. 8, 2010).
Again, Thomas More Law Center v. Obama is currently before the United States Court of Appeals for the Sixth Circuit, and is the furtherest along of any of the cases in which a judge has reached the merits of the constitutionality of the minimum coverage provision.