I know we've got a great thread for spots to hit in PDX, but haven't seen a similar one for the big city. I'll be there next week for a few days, and looking for some good spots to hit, ideally in the Belltown/Denny/Downtown area, as that's where I'll be staying, and don't anticipate having transportation....
http://beeradvocate.com/community/threads/visiting-seattle.10965/ http://beeradvocate.com/community/threads/pacific-northwest-trip-brewery-reccomendations.139991/
I'm too lazy to verify, but I don't think The Masonry is on those threads, as it's pretty new: http://themasonryseattle.com/
There is a very nice app at http://www.washingtonbeer.com/ that shows all (most?) relevant beer sites in Washington State as well as a mapping function that links to your gps.
Admittedly, this sort of cheating, but: This distro list from one of my local breweries also serves as a decent guide to beer spots, mostly on the Wet side of the state, but also some of the rest: http://www.bbaybrewery.com/#!beer-distribution/cd1d
