The Massachusetts State Archives have a clean, uncluttered homepage that promise compelling digital content.
Vital Records from 1841-1910. This is a searchable master index that displays name, town, date but does not show an actual image of the original records.
Similarly, Passenger Manifests, 1848-1891 are fully searchable and display the passenger's name, arrival date and ship name. Note that a more detailed record with information such as age and occupation, can be seen by clicking View next to the summary record.
MA Archives Database from 1629-1799 is difficult to describe, but it's essentially an extensive searchable index to 18 volumes covering discrete topics: Colonial Period, Domestic Relations, Ecclesiastical, Emigrants, French Neutrals, Indians, Towns, Maritime, Orders, and Petitions.
Elsewhere, the Commonwealth Museum hosts several online exhibits (unfortunately, in awkward slideshow format, but c'est la vie):
The Massachusetts Cultural Resource Information System (MACRIS) is a database of historic properties and areas in the state.
More typical archive materials -- photos and images of historical items -- can be found in the varied online collections of the Massachusetts Historical Society:
Keep an eye out for the lobsterbacks!
More historical archives and research materials can be found at these excellent resources:
Historical Newspaper Archives Ancestry.com
Genealogy Tools US Historical Newspapers
European Historical Newspapers International Historical Newspapers