This lovely illustrated book takes you by neighborhood around the city and describes the various street trees and their history. Each neighborhood has a single species that she focuses on, but the neighborhood map contains references for all types of trees in that area.
Just walking around my neighborhood with her book informed me of what kinds of trees I was looking at. Since most street trees are introduced from other parts of the country (or the world), I am unfamiliar with many of them.
She identifies the largest specimens in the city (by diameter), which generally are the older trees. She doesn't give the actual diameters though, which is a bit disappointing.
This is not a comprehensive 'trees of Seattle' book, since there are many trees in parks, cemeteries, and on private property that are notable. These are the street trees, planted in parking strips or within other public right-of-way. The history of how they got there is pretty interesting.
If you're in Seattle, do yourself a favor and grab a copy of this book to check out the trees in your neighborhood. It'll also give you an excuse to take a walk in another neighborhood, always a good thing to do.