Check out Orin Kerr’s Selling Liberal Constitutionalism, Jack Balkin’s What Liberal Constitutionalism Has Going For It, and Dan Solove’s Constituitonalism and Legitimacy. Here is a taste from Balkin:
In fact, Scalia isn’t really an originalist at all. He is what I would call a "New Deal/Brown originalist." That is, he is a conservative who accepts the New Deal and very basic elements of the civil rights revolution because all Americans have come to accept them, but insists that we go no further down that road. Scalia is not defending the framers; he’s actually defending a conservative version of the constitutional status quo circa 1960. There is no particular reason to defend the Constitution of 1960 from further change. It is certainly not the framers’ constitution. And it is not our Constitution.
And:
[Liberal constitutionalism’s] basic principles are simple. First, we must be faithful to the constitutional text and to the basic principles of the Constitution that underlie it. Second, we must apply and adapt these principles in the text to changing times. Liberal constitutionalists from Brandeis to Brennan have made these two basic claims over and over again: Be faithful to the constitution’s text and principles, and apply them faithfully to new circumstances and new challenges.
Perhaps most important, these principles aren’t particularly liberal principles. They are constitutional principles that both liberals and conservatives can accept. If you wanted a slogan for a twenty first century constitutionalism, that would be a pretty good start.