Orin mentions the response by scholars and government officials to the DOJ "White Paper" on the wiretapping program. Two additional points bear mentioning. First, this same group issued a letter on January 9, 2006 that laid out their views; the DOJ white paper responded to that, and their February 2 letter responds to the DOJ memo.
Second, and more importantly, this is an impressive group that includes distinguished people from different political camps. At least three are not on anyone's definition of the conventional political left -- Curt Bradley, Richard Epstein, and Bill Van Alstyne. And, for what it's worth, Bradley was the Counselor on International Law in the State Department Legal Adviser's Office for 2004 (it's a one-year position, chosen by the State Department Legal Adviser).
Perhaps in the best of all worlds this point about the signatories would be irrelevant, and each of us would evaluate the arguments without regard to who made them. But in a time-starved (and politically charged) world, the identities of the signatories often is significant. And here the breadth of the signatories is notable.