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.
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!