I've been reading the discussion of John Rawls by Will (here and here) and Sigrid (here and here), as well as the Richard Epstein tribute to Rawls that Will quotes in his first post.
Rawls' theory, I think, suffers from the fatal flaw that his "justice as fairness" ideal, and the "veil of ignorance" experiment that embodies it, could support a very broad range of moral/political systems. The imperatives Rawls derives from his machinery are just one of many sets that it could produce. A Theory of Justice seems a sort of moral Rorschach test; in its pages, almost any reader can see whatever political system he or she prefers. Consider what Epstein writes in his NRO tribute: "Rawls's framework could easily and sensibly be pressed into service by those who had more utilitarian objectives."
In Beyond Good and Evil, Friedrich Nietzsche (who gets my vote as the greatest philosopher of the last 200 years) offers this critique of philosophers' use of elaborate theoretical machinery to support their moral theories:
They all pose as if they had discovered and reached their real opinions through the self-development of a cold, pure, divinely unconcerned dialectic (as opposed to the mystics of every rank, who are more honest and doltish—and talk of "inspiration"); while at bottom it is an assumption, a hunch, indeed a kind of "inspiration"—most often a desire of the heart that has been filtered and made abstract—that they defend with reasons they have sought after the fact. (BG&E, Aph. 5; Kaufmann's translation)
Few people today read Nietzsche, and even fewer read him well. If you're a libertarian who's into Ayn Rand, treat yourself to a copy of Nietzsche's Genealogy of Morals.
And to answer Will's other survey question: The Beatles. Not even close.