Beside the space needle they have another center of some type, they had a Chihuly glass exhibit-it is still there until the middle of March at least. It was pretty cool to see, go at night though then you can walk through the glass outside at night, it is all lit up.
You can buy a combo ticket and do the glass at night and come back the next day and do the space needle. There is a small monorail behind the space needle that will take you a little closer to down town and back again, cost a couple of bucks. Parking is a little cheaper near the space needle.
There is a science center as well, when we were there they had the King Tut exhibit on, might want to see if they have something interesting-if there is no special exhibit there that interests you I would skip it, was mostly for kids from what we saw.
Pikes Place is obviously a must, some cool stores, like a farmers market. Super super cheap flowers-the fresh cut flowers in there go for blocks. Very first Starbucks ever is also on the same street. Cool just to walk around downtown as well.
If you drive stick downtown-be aware, there are LOTS of very steep hills with lights at the top, and I mean steep. The taxi cabs all have bushguards on the front of their cars and will pull up right behind you. I have driven stick for 15+ years and was a tad uncomfortable with this arrangement. Down the hill from Pikes Place Market is where all the cruise ships pull in. Sometimes you can find parking down there, you will have to pay anywhere you go. Downtown Seattle parking rates are like Calgary.
The Woodlands Park Zoo is nice as far as zoo's go, comparable to ours.
There is a big shopping mall downtown, I would skip it. A lot of the stores are the same that we have here.
We ate one night at Gorditos, it is somewhere not downtown lol, burritos as big as babies. Pretty good Mexican food.
I have been there about half a dozen times but have friends that live outside of Seattle so usually stay with them.
Oh and Washington State Ferries are relatively cheap compared to BC ferries if you need to take one.