I honestly can't think of a liberal equivalent of Rush Limbaugh. There might be one or two liberals who have made similarly controversial remarks, but none of those liberals have the party influence Limbaugh enjoys, nor the moral/lifestyle hypocrisy. Wolcott:
[Michael] Moore was too independent an operator to be seamlessly morphed with Al Gore and John Kerry. But Limbaugh bleeds Republican red. He has been glorified and embraced as the perfect Ganesh by Newt Gingrich, CPAC, and the Bush family. He is the face and mouth of the conservative movement. A mouth that has swallowed Michael Steele whole, and has room for plenty more.
I really can't think of a 1:1 equivalent.