There are quite a few green networking groups in Boston these days, but I've consistently heard great things about Net Impact. It is a membership-driven organization, but their events are open to the public. Net Impact is a global organization that brings together people from different sectors on a mission for social and corporate responsibility. They host a variety of educational events, details of which can be found here. The group is best known for their monthly Sustainability Breakfast - what an inspiring way to start the day!