Don and Debbie,
Not much I can add except to second several of the votes given here. We go south about once every 3-4 years and love Gig Harbor, Penrose Point State Park, Jarrell Cove State Park, Blake Island State Park (either at the marina or on the backside on a buoy), Bell Harbor Marina, McMicken Island State Park.
I would add Tacoma—Dock Street Marina is right downtown and has easy access to the Museum of Glass, Washington State History Museum and a great waterfront promenade. If you get as far south as the Olympia area, the little town of Boston Harbor at the north end of Budd Inlet is a neat little stop. And Olympia has a great Farmer's Market, but it is closed from Jan-Apr. Of course, if you stop at Bell Harbor, you'll be right at Pike Place Market in Seattle.
Also pushing the definition of South Sound, Winslow on Bainbridge Island is a nice town in a well-protected harbor and Poulsbo is a charming town with a strong Norwegian heritage. We just spent the Thanksgiving weekend there. If weather forces a stop on the way down, Kingston and Edmonds are nice stops as well.
If you do stop in Bell Harbor and are up to it, give me a call. We'd love to meet you for dinner or something. We're just right up the hill from downtown.