Michael Sandel, who is a critic of the left from within the left; Robert Putnam, whose work tends to ratify a lot of conservative insights about social order; William Galston, one of the few liberal students of Allan Bloom who respects and engages conservative perspectives; and Alan Wolfe on occasion.
John Rawls deserves respect and serious reading, as he attempts to justify aggressive egalitarianism within the liberal tradition instead of tearing it down like Marx and today’s nihilist postmodern left. Even if his premises and major steps are wrong, he is the key thinker for much leftist thought today, though I find that few leftists have read him carefully.
Finally, Cass Sunstein is the most sophisticated political-legal thinker on the left, and he is dangerous precisely because he can synthesize conservative thinkers like F. A. Hayek into his leftist agenda. I used to enjoy the prose style and unusual arguments of the late Murray Kempton. He was the left’s closest equivalent to William F. Buckley Jr., and some of his old columns are worth reading.