GMU law professor Ilya Somin has this take on the constitutionality of the health insurance mandate, which concludes if nothing else that the challenges to the mandate are not frivolous and what the law requires is something new, for which there is no binding precedent upholding its legality. Professor Barnett from GULC has this paper that concludes the individual mandate is unconstitutional.
By contrast, in this Bristol paper article about the lawsuit against the health insurance mandate filed by Gil Davis and Strother Smith on behalf of Smith, Tucker Davis and others, W & L law professor Tim Jost describes the claim as frivolous.
There is a website devoted to the litigation of this issue, called Health Care Lawsuits.