Regional bus service is relatively plentiful throughout western Massachusetts. It can be a handy and somewhat affordable means of getting around, as buses travel many routes that trains do not; however, this style of travel prevents the sort of spontaneity and freedom to explore than what you're afforded if traveling by car. It's a good idea to compare travel times and costs between bus and train routes to and within the Berkshires; in many cases, it's faster to take the train.
Bonanza Bus Lines connects Sheffield, Great Barrington, Stockbridge, Lenox, Lee, Pittsfield, Brodie Mountain, and Williamstown with Albany, New York City, and Providence. Peter Pan Bus Lines serves Lee, Lenox, and Pittsfield from Boston, Hartford, and Albany. Berkshire Regional Transit Authority provides transportation throughout the Berkshires.
Reservations are not required on buses serving the region, but they're a good idea for just about any bus trip.