The State Library of Massachusetts has digitized their collection of early Massachusetts Registers, and made them available to the public. Spanning the years 1767-1878, these volumes are part almanac, part directory -- phone books before there were phones, if you will. They are a fantastic resource for researchers.
The almanacs are also an invaluable resource on Massachusetts state and city/town elected officials, justices, lawyers, sheriffs, ministers, and officers of various organizations throughout the state; institutions such as schools, churches, and societies; area businesses; soldiers; and military activities. In earlier volumes, it's common (and exciting!) to come across such famous names as John and Samuel Adams, John Hancock, George Washington, James Bowdoin, and others.
One interesting feature found within the 1862 register is a lengthy section titled "History of the Rebellion and Massachusetts Action", which covers state, legislative and military action, noteworthy men, and the historical events leading up to the beginning and early years of the Civil War through 1862. A substantial part of this section provides a complete account of the Massachusetts Volunteer regiments, including sketches about each regiment and lists of soldiers' names accompanied by the Mass. cities and towns from which they hailed.