The North Shore, Boston, Cape Cod, and South Shore are all good place to start out on an afternoon boat trip.

Boston Harbor Cruises - Offers several options including Boston Harbor, lighthouse and Charles River cruises.
Cape Ann Lighthouse Cruise - A feature from BellaOnline on touring Annisquam, Thacher Island Twin, Eastern Point and other North Shore lighthouses.
Charles Riverboat Company - See the Charles River and Boston Harbor by private charter or on a sunset cruise.
Essex River Cruises - Explore the salt marshes and wildlife on the North Shore along the Essex River.
Horizon's Edge Casino Cruises - This casino cruise leaves from Lynn, north of Boston.
Hy-Line Cruises - Cruises from the Cape to Nantucket or Martha's Vineyard. They also offer harbor cruises, deep sea fishing, and trips along the Cape Cod Canal and by the Kennedy Compound in Hyannisport.
Massachusetts Bay Lines - Music cruises and whale watches on Boston Harbor.
Newburyport Whale Watch - Besides whale watches, the Prince of Whales also sets of on regular sunset cruises and trips to the Isles of Shoals.
Plymouth Harbor Tours - Explore Plymouth Harbor on board a Mississippi-style paddlewheeler from Captain John Boats.
Princess Yacht Charters - A private charter vessel that sales from Boston Harbor.
Schooner Thomas E. Lannon - This ship offers daily boat rides from Gloucester Harbor.
Yankee Clipper Harbor Tours - See Newburyport Harbor during a daytime or sunset cruise with Captain Bill Taplin as your guide.