As if on cue for our class, the President yesterday issued his first signing statement in signing the omnibus budget bill (for fiscal year 2009) into law. In doing so, he declared that several provisions of the bill were unconstitutional intrusions on his presidential authority, and that he would decline to enforce them.
The President's constitutional objections varied (as might be expected given the sprawling nature of the bill). One provision, which dictates that no federal funds can be spent on NATO peacekeeping missions where U.S. troops are placed under the command of a foreign commander, President Obama declared interfered with his powers as commander in chief and unconstitutionally constrained his authority in diplomatic negotiations. Other provisions, which stated that money could not be spent or reallocated without the consent of congressional committees, effectively amounted to legislative vetoes. The President called these "impermissible forms of legislative aggrandizement."
You can find President Obama's signing statement here. And you can find an article from this morning's New York Times on the signing statement here.