The Federalist Society has a very good discussion up on the Medellin case. Part I (which deals with the Court's conclusion that the treaty obligations in the case were not self-executing) is here, Part II (dealing with the presidential powers issues) is here. I've only read Part I at this writing; that segment is quite good, with the great rising scholar Nicholas Rosenkranz (among others) delivering a beatdown on Medellin critic David Sloss.
Incidentally, if you haven't bookmarked Originally Speaking, the Fed Soc's main debates page, you should.
(Hat tip: Orin Kerr at Volokh Conspiracy)