Because of its expansion through annexation and land reclamation, and because of the vast differences in size between its neighborhoods, making a web-ready neighborhood map of Boston is extremely difficult. Most online neighborhood maps currently available are simple line drawings or text paste-overs.
I've attempted to solve both these problems by creating a neighborhood map of Boston using Google Maps. It overlays the neighborhood boundaries onto Google's existing maps, and scales easily in and out.
Plus, unlike other nifty Boston Google Maps, which are script API-based, mine is readily embedable into any webpage, and plays nicely with other user-generated Google Maps content, so you can create mashups—here's a screenshot of neighborhoods and foreclosures (I don't think Google lets you you link to mashed-up user-generated maps...yet).
I've probably gotten some of the neighborhood lines wrong, so don't hesitate to email me corrections. My site also uses an Object element to insert the maps, so your mileage may vary with Internet Explorer. Do yourself a favor and download Chrome.