I guess anything besides beer breweries...
Besides Sam Adams, I did:
Fenway tour - liked it, but it really depends on your interest level in the sport
NE Aquarium - pretty good, but not a great 'value' given the prices
Duck tour - also pretty good, but I imagine a lot of the enjoyment was due to great weather
Freedom Trail tour - it was pay what you want, liked it but again might not be as enjoyable in winter weather
USS Constitution - ship itself was good, museum was even better
Boston Common - just walked around the gardens, nothing special