I know you said Portland ,but Seattle isn't that far...
I am a Chocolatier with Dove Chocolate Discoveries (TM) in the Seattle area which is great chocolate ,but there are some amazing chocolate makers here that are worth the trip like...
Rocky Mountain Chocolate Factory
Theo Chocolate Inc
Chocolati Cafe Wallingford
We also have the International Chocolate Salon on July,11th 2010 where you could meet and eat from them all.
If you make it to Ann Arbor, you must make a stop to Zingerman's Deli. They have a great Chocolate Lady, Duff, who can show you their outstanding retail department. They don't make their own candy but do make their own gelato and baked goods. I don't remember the company's name, but Duff carries a "truffle of the month" from a local candy maker. Ask her for the details and she can lead you to all the local foodie sights worth seeing.