RIGGSVEDA has an interesting post at The American Street. Riggs answers the challenge put out by Eric Alterman to come up with five basic principles of liberalism. That's easy, says Riggs:

1. Equity: equal treatment; equal worth; the end of favoritism and the worship of wealth and power; the same consideration given to the needs of the weak and few as to the strong and many; an even hand in foreign policy and trade towards nations strategically important to us as well as those which are small and economically insignificant.
2. Justice: Where inequity exists, it is removed, and where wrongdoing is found, it is stopped and retribution is made, regardless of status or connections; nations engaged in murder, repression and genocide are held to account, even if they are allies or strategically important, and even if it means some sacrifice on our part.
3. Mercy: Punishment is a means to rehabilitation, not vengeance; help is given to those in need, and is a social debt we each owe to the community of our common humanity; empathy and refusal to judge others are the building blocks of socila interaction.
4. Humility: Recognizing that we don’t always have to be the biggest, the best, the strongest, the wealthiest, the most favored by God; that we have obligations to the natural world; that we are interdependent with other animals, plants and nations, and that we survive because of them whether we are aware of it or not.
5. Intelligence: That a love of knowledge and curiosity about the world is what animates us as a race, and is to what we owe everything we are; that real education is a right as surely as life, liberty and the pursuit of happiness; and that a free market without free education is merely a bazaar for auctioning off wage slaves.

I agree that the five principles above are essential to a liberal worldview. That said, I would add two more:

Perspective: The recognition that any individual's perception of what is important and true is strongly influenced by demographic factors beyond his or her control: what country s/he was born in, what part of the country, what city, what part of that city; what family she or he was born into or raised in, whether the individual even had a family or grew up in foster care; what socioeconomic conditions the individual grew up in, what religion, what ethnicity, what nationality. If you grow up white and upper middle class in Orange County, California, you will not have the same deeply held beliefs about what the world is like, about what is important and what is not, about what the possibilities of life are; as you will if you grow up white and working class in rural Tennessee; or as you will if you grow up black or Latino on the South Side of Chicago or in the Mott Haven section of the Bronx. Truth IS relative. You can call it the Hamlet principle: There is more in heaven and earth than is dreamt of in your philosophy. If you believe that truth is absolute and there is only one correct set of beliefs and only one proper way to live, then you are not a liberal.

Process: The recognition that the way you go about reaching a goal is as important as the goal itself; and the companion recognition that no accomplishment or success is praiseworthy if the means used to achieve it is wrong or harmful or destructive. You can call this the Gandhi principle: There is no way to peace; peace is the way. If you believe that peace is the moment after the enemy surrenders and the bombs and gunfire stop, you are not a liberal. If you believe that war and violence lead to peace and understanding and cooperation, you are not a liberal.