1. Kerry Park - Every photographer in Seattle must visit this spot! It has great views of downtown Seattle and the space needle. Kerry park tends to be a little windy - so a sturdy tripod will be very useful. There are a number of interesting compositions here - Space needle with downtown Seattle, Space needle by itself, Space needle with downtown Seattle and Mount Rainier.
Don't be afraid to experiment with your composition. After sunset you can also try different compositions with the full moon. Check the lunar calendar to determine when there is a full moon. The best sunset colors are usually in summer but some of the most delicate hues are in spring - usually the day before/after a storm. The picture below was taken after a spring storm
2. Betty Bowen viewpoint - This little known viewpoint is only a few blocks from Kerry Park along Highland drive. It has sweeping views of the ocean and the magnolia marina. In my experience I have found this to be a better spot to shoot sunset colors that Kerry Park.
Directions to Kerry Park
3. Kinnear park - Refer to this blog post -