I suppose, a copy of the Constitution might be an appropriate gift to give the Chief Decider (if you're on a budget, you can go with the just the Bill of Rights)
A Law Day Unto Himself; Beyond Presidential Power, What Is Bush Upholding?
And, speaking of budgets ...
IRAQ WAR: Price tag for war in Iraq on track to top $500 billion
Proclamation by the President: Law Day, U.S.A., 2007
Bill of Rights Institute
The Constitution of the United States
Email the President a Happy Law Day greeting