My biggest disappointment on this visit to Seattle was that the Odyssey Maritime Discovery Center had closed. It's under new management, mostly used as a rental facility, and now called the Maritime Events Center. The exhibits are still there, but the museum is only open when they have corporate sponsorship for school visits. They'll be open several Mondays in the spring of 2010, but were closed all of our vacation. Their schedule should be listed at http://maritimeeducationinitiative.org/.
The museum has some of the best interactive exhibits I've ever seen, and as a museum professional, I have seen many. They have a sea kayak with ores. As you move the ores, a video travels across Elliot Bay. They have a model crane to move containers on from the ship to the train. My daughter's favorite is the Water Table with pegs and panels to create your own dams and model locks. I learned more at that museum than at any other pair of museums worldwide, mostly because the information is clear, not overwhelming, and limited to the natural and human specifics of Puget Sound. It's located right next to the aquarium. I highly recommend a visit, if they're open.