I think my favorite case in Federal Income Tax was Eisner v. Macomber, since I frankly found the boundaries of Congress's taxing authority far more interesting than hair-splitting about life insurance, sale-lease-backs, or the characterization of loss. So I am quite interested to see, via Eugene Volokh and Orin Kerr, that the D.C. Circuit has declared a small portion of the Internal Revenue Code to exceed Congress's power to tax income. (The case is called Murphy v. IRS, and the opinion is here.)

I have not yet read the decision and probably will not until I hit the library tomorrow.