That is where I spend my school lunches, after school days, and weekends along with my friends. Grinds and slides go very smoothly because the ledges all over the skatepark have an L-shaped metal coating, which keeps it nice and smooth. Other than the park, there are only two other good spots I can think of. At the end of the tables there is a small bench, which is about three feet away from the tables so you have to gather some speed to your trick in order to clear it. These are my favortie spots, there are others along the main industrial road called Pacific Highway where there are banks, hotels, and other businesses around with architecture that looks like it was designed by a skater, for a skater.
Downtown is, as in most cities, the main skating spot source.
Downtown Seattle is pretty sweet, but of course pigs are all over the place so good luck sessioning at one spot for over half an hour. The scene here is awesome with everyone being cool to one another and just down for skating.