The Stanford Libraries have recently acquired two new interesting microfilm collections of manuscript material dealing with 19th century American History:
The Horace Greeley Papers, 1831-1873 and the John Patterson Green Papers, 1869-1910.
An online guide to Greeley's papers may be found on the Primary Source Microfilm Scholarly Guides site (scroll down to the entry for Greeley's papers).
Green, a prominent Ohio African-American legislator often known as the "Father of Labor Day" has a helpful biographical sketch in the Encyclopedia of Cleveland History.