Eat lunch at the Crab Pot. Get their signature dish. it's awesome!
Walk around Pikes Place. Visit the fish shop that throws fish, and just a few stored down have a beer in the place where Tom Hanks and Melanie Griffen made that movie. There's a bar in the back with GREAT views!!!!!
Go hiking in Steven's Pass. i prefer Lake Serene. BUT be warned. It's not easy and takes a good 7-8 hours for the whole hike. VERY worth it though.
Visit some of the Bikini coffee shops. My fav was in Monroe (1.5 hours NE of Seattle). Not sure it's there any longer though.
If you have time and in season get a charter boat and go salmon fishing.