The Massachusetts Archives Digital Repository contains many historic documents, records, photographs, maps and more. You can now search by keyword or browse the archives on their website at http://digitalarchives.sec.state.ma.us/.
Below is a list of the items available online, although much more is available at the Massachusetts State Archives. Hopefully they will be adding more soon!
Some items available at this time are:
Massachusetts Town Plans 1794-1795 (maps with street names) [Link]
Massachusetts Town Plans 1830 (maps with street names) [Link]
Index of Massachusetts casualties in World War II. [Link]
Registers of Vital Records 1841-1925 [Link] At this time contains only 1916 Deaths [Link] and Death Certificates from the Great Molasses Flood of 1919 [Link]