For the OP, here is a sampling of theologians, bible scholars and others who could be included in the category of liberal Christians. Some of these I would consider moderate, but traditionalists and conservatives may categorize them as liberal. A lot depends on point of view. Many are Catholic, but not all. I will mark my favorites with an asterisk, which means I like what they wrote and I can, for the most part, understand it. No particular order:
John Shelby Spong* - Episcopal bishop, bible commentary
Bart Ehrmann - You can find talks and lectures on the internet
Brian McLaren - Bible commentary
Wilfred Cantwell Smith * - Christology and other stuff
Jaroslav Pelikan *- Orthodox and Lutheran background; Bible commentary
Harvey Cox - opinions on just about everything; very readable
N.T. Wright - Anglican bishop, NT scholar, moderate theologian
Marcus Borg* - NT scholar
Gordon Kauffman, Mennonite theologian, great insights
John Hick, theology and Christology
Here are some Catholic theologians and scholars that would be considered liberal (many of them investigated by the Vatican's doctrinal police):
Jacque Dupuis, S.J. (Jesuit), theology and Christology
Hans Küng*, theology, Christology, scripture, etc.
Gerald O'Collins, S.J., Christology
Roger Haight, S.J., Christology - difficult reading, IMHO
Geoffrey Robinson, Bishop from Australia - vocal on the issue of abuse and a critic of the institutional Church
Garry Wills*, historian - lots of interesting takes on what Jesus meant, Paul meant, etc.
Albert Nolan, Dominican, wrote about "Jesus before Christianity"
Louis Evely*, speaker and writer on spirituality; wrote "The Gospels without Myth" - Vatican didn't like it
Anthony DeMello*, in the mold of Evely, preached with stories and parables, kind of like another guy from 2000 years ago.
Then there are the Liberation Theologians, mostly but not all from Latin America:
Gustavo Gutierrez - one of the fathers of Liberation Theology
Leonardo Boff* - critic of the Church hierarchy, which in turn criticized him
Jon Sobrino - another major proponent of LT
Tissa Balasuriya* - Sri Lankan theologian, Christology, Mariology and Liberation Theology; so radical he was excommunicated for a time.
Dom Helder Camara* - Archbishop in Brazil; not a theologian but a big supporter of Liberation Theology; his short book "Through the Gospel" is a great spiritual read, with social, political and religious commentary to spice it up.
Oscar Romero - Archbishop in El Salvador, spoke out for the poor and in defense of his priests who were being killed by the government; so they assassinated him (and then probably went to Mass the next Sunday and took Communion - oops, did I say that?)
There are many more, including several women theologians and scholars that would likely be put in the liberal bucket, such as Elizabeth Johnson, Margaret Farley, Rosemary Radford Ruether, Marina Warner, Ilia Delio.
So start reading now, and check back in five years or so to tell us what you've learned about Liberal Christian view points.
Note: if I mislabeled anyone, misspelled names, or forgot key people, I apologize.