Dr. Martin Luther King, Jr.'s speeches are as relevant today as they were when he wrote them, because we still face the same problems and people haven't changed. Another great American whose words are still valuable is less quoted: Eugene Debs.
This is probably his most famous quotation:
"Years ago I recognized my kinship with all living things, and I made up my mind that I was not one bit better than the meanest on the earth. I said then and I say now, that while there is a lower class, I am in it; while there is a criminal element, I am of it; while there is a soul in prison, I am not free."
--Eugene V. Debs, Founder of the American Railway Union