The branch of philosophy that is devoted to considering values and value claims is ethics. Ethics can cover both personal ethics and the ethics of policy considerations. The branch of law that is devoted to considering ethics with respect to the law is jurisprudence, the fancy way of saying philosophy of law and the ethics of law.
It strikes me that philosophy, including as it does ethics, is an inescapable part of life, especially when we turn our attention to debates about values.
But whereforth are thou, philosophy?
When we turn our attention to works in public philosophy, Nussbaum's new book about sexual orientation, mentioned above, should be of interest to liberals.
Liberals should also welcome James H. Fetzer's book RENDER UNTO DARWIN: PHILOSOPHICAL ASPECTS OF THE CHRISTIAN RIGHT'S CRUSADE AGAINST SCIENCE (2007). In this book centered on the debate about teaching evolutionary theory in public education, Fetzer also has a fine chapter on the abortion debate, in which he works with deontological moral theory to work out his position supporting legalized abortion in the first trimester.
Regarding broader political orientations, liberals might also enjoy reading Alan Wolfe's book THE FUTURE OF LIBERALISM (2009).