Although I prefer the selection in farmers markets here in San Francisco, the Haymarket in Boston gets points for reminding me of shopping in the chaotic markets in Rome. The prices are cheap for Boston, but that's not saying much ;)
To avoid a wasted trip into town: It's more of a place to get run of the mill produce and meats at cheaper prices than a place to find artisan or organic goods. I recommend going early since the produce gets picked over by the end of the day (and the street starts to smell).
