Don't forget The Mountain Shop (http://www.mountainshop.net/) and Next Adventure (http://nextadventure.net/) (the latter also has used gear). Next Adventure is a dealer for ULA packs. Oregon Mountain Community has already been mentioned.
Also, check out Ron Moak's Six Moon Designs (http://www.sixmoondesigns.com/) out west of town in Beaverton, which makes excellent lightweight packs and shelters. They are a "cottage" manufacturer, not a retail store, so call a few days ahead for an appointment. It is possible next Tuesday that Ron may not be back from the Pacific Crest Trail Kickoff in southern California, but surely someone will be around!
I recently discovered "Only The Lightest Camping Equipment," in Troutdale (east on I-84). (http://www.hikelight.com/index.html) It has been around for years but somehow I hadn't discovered it. I haven't been to visit yet, but plan to go soon. They are mail order and carry lots of lightweight and cottage manufacturer gear. A lot of the "cottage" gear is from Six Moon Designs across town. Again, I'd call a few days ahead for an appointment. If you can't get to both this and Six Moon Designs, hit Six Moon first!
Finally, backcountrygear.com in Eugene is great. I've had excellent customer service from them. Every time I order, "Brown" brings the package to my doorstep the very next day. They do have a retail showroom you can visit.
Box up the rest of your gear and take it with you so you can try the packs on with your gear inside. Ron Moak of Six Moon Designs will insist on this, and I'm sure the other places will be happy to help you, too. There's a lot of difference between sandbags and the gear you're actually going to carry!
Of course there's the downtown (Pearl District) REI. I've never had much luck with lightweight gear there, but it still might be worth a look. Don't bother if you've been to the one in Eugene.