Other than Pro Mountain Sports, there are no shops in Seattle that specialize in UL or carry "cottage" gear. I find it very odd considering the hiking activity in the region, but there are very few UL-centric stores in the world. We are forced to go at it piecemeal
Second Ascent in the Ballard area is very good and has a lot of UL products although it isn't their focus. They take used gear for store credit and sell a lot of used gear. They carry climbing, ski, and bike gear too. Nice folk to deal with.
Outdoor Research has a company store in the SODO area and annual parking lot sales. The Filson company store is close by. Outdoor Emporium is a "hook and bullet" store next door.
Arcteryx just opened a store downtown. Patagonia, North Face, Eddie Bauer, Columbia, and Mountain Hardware have stores there too.
Ibex has a store in the University Village mall. Edie Bauer and North Face have stores there as well.
Marmot Mountain Works in Bellevue is a good hiking gear resource.
And of course there is REI.
If you get up to Vancouver, Canada the MEC store is a must see.
Backcountry Essentials in Bellingham is a great small store. Do check out the used gear on the second floor.
The Mountaineers will have a Gear Grab sale 9/30 from 6-9: http://www.mountaineers.org/stories/news.cfm?reader=275