To make an rather boring and predictable point, it depends on definition of "liberal", assuming we are using the term to mean "left-wing", I can't think of many. I know Cao voted for the stimulus, but I can't think of any current Republican that would fit in with the *old Republican party of the mid to late 1800's (pro-tariff, anti-trust, anti-big business).
*I understand that these aren't universal principles of that century's Republican Party (namely the likes of Rutherford Hayes and James Garfield)
late 19thc GOP: anti-monopoly? yes. anti-big business? no.
as for the original question: Snowe.