Try to come during the week when the factory is in operation. The story of how Ben and Jerry got started with a $5 correspondence course and an open book exam is quite funny. The tour is full of humourous stories related to the company and its founders.
The tasters at the end of the tour were quite popular. Of course, you have to have ice cream at the end of the tour. My favorite was the Chunky Monkey, although my favorite name had to be the Chubby Hubby. If you are in the area, there is a great stop at a combination shopping area with specialty shops of teddy bears, cheese, and chocolate on the right just before Ben and Jerry's coming from Stowe. Also worth stopping in at is Cold Hollow Cider Mill.