Later on in my work-free day in Portland, Oregon, USA, I stopped by the Mill End Store (www.millendstore.com/). I was meeting a friend in Milwaukie for dinner, and he had recommended this place. Their selection is large, but a little less comprehensive than Fabric Depot. The entire store is basically a clearance section, so their prices are excellent. If you're looking for something in particular, you might not find it though. I saw some great silks, a decent stock of Asian-print cotton suitable for Wafuku, and (at least right now) a large selection of linen in some amazing colors.
If I hadn't already spent a bunch of money at Fabric Depot (and Powell's Books), I probably would have bought a pile of stuff here. As it was, my luggage barely made the weight allowance.