On seeing part of a documentary about the “Freedom Riders” of the ’60’s, I heard mention of several rabbis who had participated. I confess that this was new information to me. So, I began compiling a list of their names (arranged below alphabetically by last name) from any articles I could find:
Rabbi Saul Berman
Rabbi Israel Dresner
Rabbi David Forman
Rabbi Martin Freedman
Rabbi Joseph Henry Gumbiner
Rabbi Arthur Lelyveld
Rabbi Allan Levine
Rabbi Perry Nussbaum
Rabbi Walter Plaut
Rabbi Philip Posner
Rabbi Allen Secher
Rabbi Sidney D. Shanker
Rabbi Matthew Simon
Rabbi Ralph Simon
Rabbi Herman S. Stern
Rabbi David Teitelbaum
Rabbi Andre Ungar + wife Judy
Rabbi Abraham Joshua Heschel marched with Dr. Martin Luther King in Selma, AL, but I don’t yet know if he participated in any of the “freedom” bus-rides, too. Other rabbis were likewise active in the Civil Rights movement, but might not have been “Freedom Riders” per se.
I haven’t yet seen anyone listed with the title “Cantor.”
No female rabbis are mentioned; the first woman wasn’t ordained until roughly 25 years after the “Civil Rights” era of the late ’50’s and early ’60’s.
The “Freedom Riders” consisted of “…436 riders on more than 60 rides throughout the South. The rides took place from May to November in 1961…About half of the 436 riders [@218] were white, and of the white riders roughly 25 percent [@54] were Jewish. Not all of them were rabbis…”  I’ve found the names of 17 rabbis — i.e. @ one third of the Jews who rode.
436 riders in total. Talk about a handful of people changing the world!
This might not be a complete list. I will add to it as I find more names. In addition, there were, of course, other Jews involved as well — especially Michael (Mickey) Schwerner and Andrew Goodman, who, along with James Chaney,  were murdered for their participation. That would be a harder list to compile accurately and fully; the attempt should be made.
These rabbis (and one rebbetzin) were making a specifically Jewish/religious statement about civil rights, as well. Over time, I’d like to add some biographical data for each rabbi. Have anything to contribute? All information welcome, as long as its verifiable.
Among the many good online articles on Jews in the Civil Rights movement are: http://rabbiallensecher.com/freedom_rider http://www.thejewishweek.com/arts/film/rabbi_was_freedom_rider
(I received a subsequent note from Rabbi Allen Secher:
“I was involved in two different jailings — Albany, GA (Aug. ’62) and St. Augustine, FL (’64). I’ve attached the names of the participants.
I think that [Rabbi] Sy Dresner’s mention in the Documentary referred to the Albany gathering. To the best of my recollection, no rabbis were involved in the ’61 rides.
Many of the rabbis on your list were involved in subsequent marches — Selma, etc.
There’s also a written piece from ’64 called “Why We Went.”
Hope this is helpful.”)