I will put in my nomination for Ancient Wonders, which is in Tualatin (suburb south of Portland), just off I-5. Good selection, tends to have a lot of older RPG stuff as well as Warhammer, CCGs, some comics, and boardgames. The staff is usually very helpful there.
While Bridgetown is a nice store as well, my experience is that they primarily consider themselves a model shop, and aren't really that familiar with RPGs. I've also had others tell me that they aren't very enthusiastic about their Warhammer product, but that's hearsay. However, the staff is pleasant (not the stereotypical overweight antisocial guy behind the counter).
There's also Rainy Day Games, in Aloha (west of Portland). I've never been there myself, but heard good things.
Generally speaking, although there aren't as many gaming shops in Portland as there used to be a couple of years ago, the ones that are left are pretty good.