Judaism began in a place and time when slavery was an accepted practice. Jews have both owned and been slaves in societies where it was a legal and accepted practice. Jewish beliefs on slavery evolved over time. One key piece of the Pesach ritual is the exhortion to "remember you were slaves in Egypt". According to Torah after seven years, any slave was to be given the choice of freedom or continued slavery. Slaves were to be freed on the Jubilee year.
However, there were Jewish slave owners in the U.S. southern states when it was legal. And there were same prominent Jewish abolitionists. "In 1861, Jews constituted roughly 0.2% of Southerners (20,000 out of 9 million) and 0.3% of slaveholders (5,000 out of 1,937,625)." 
Of course the lists below are incomplete and focus on prominent representatives of the different groups regarding slavery in the Americas (mostly from Wikipedia):
Jewish slave owners: Aaron Lopez Francis Salvador, Judah Touro, Haym Salomon, Judah P. Benjamin. 
Endorsed slavery: Rabbi Morris Jacob Raphall, Rabbi Isaac Leeser and Rabbi J. M. Michelbacher
Jewish U.S. Abolitionists: Isidor Busch, Michael Helprin, Rabbi David Einhorn, August Bondi, Michael Heilprin
Jewish Abolitionists in other countries: Adolphe Crémieux, Granville Sharp, Rabbi G. Gottheil of Manchester, Dr. L. Philippson, Rabbi M. Mielziner, Berthold Auerbach, Heinrich Heine, : Theodore Wiener, Jacob Benjamin, Ernestine Rose, Nathan Mayer Rothschild
Some anti-semitic groups claim that Jews were the major players in the slave trade and owned more than half the slaves. These claims don't tend to have the backing of more neutral data such as the census information, and several come from sites with significant content from people who also oppose civil rights.
- Moses E. Levy of Florida: A Jewish Abolitionist Abroad by Chris Monaco (?), Excerpt: "Perhaps the most glaring manifestation of Levy's dual nature was his status as slaveholder and ardent abolitionist. The fact remains, however, that Moses Elias Levy of Florida -- one of the few Jewish plantation owners in the entire South -- was the author of an abolitionist pamphlet published during an extended stay in London in 1828."
- MyJewishLearning on Jews in the Civil War: Addressing the moral question of slavery. by Norman H. Finkelstein
- Time Magazine on How Do We Fight Xenophobia? by Cornel West, Professor of Religion at Princeton University and author of Race Matters
Civil rights and Martin Luther King
- American Jewish History: A Long Tradition of Social Justice by Rabbi Melanie Aron
- an article on the Religious Action Center (RAC) of Reform Judaism on A Special Bond: Martin Luther King, Jr., Israel and American Jewry by Stuart Appelbaum
- ChristianActionForIsrael.org on "Anti-Zionism = Anti-Semitism" quoting a letter by Dr. Martin Luther King Jr.
- Political Mavens.com on Dr. Martin Luther King Jr. and Jews by Heather Robinson