I just wanted to alert everyone that this is happening this weekend, because it hasn't been that well advertised, and last year it occurred in September. The festival happens at Seattle Center this weekend, starting Friday. $20 gets you admission and 10 tickets; beers cost 1, 2, or 3 tickets each, and more tickets can be bought for $1. It's a little pricey, but the reward is you get to taste a number of Belgian beers on draft, which is an entirely different thing than buying the bottled varieties, even at places that try to keep it fresh. Last year, some of the Belgian ales had unbelievable complexity. I've tasted a good deal of beer, and these were some of the best I've ever tried. They're hard to even describe, but think of layers of various fruits along with various complex herbal and sweet or sometimes sour notes; one mark of a well-made Belgian ale is that while the alcohol is usually considerable for beer (mabye 8-10%) you shouldn't be able to taste it. They'll have trippels, strong ales, lambics, brown ales, etc. Note that about half the beers will be served out of the bottle--I'd avoid those, since you can get them cheaper at places like Bottleworks, and they're not necessarily any fresher. I also place a lower priority on tasting the some of the microbrewed versions, because you can get those reasonably fresh here even in the bottle, although side by side comparisons of Hair of the Dog Trippel vs an authentic Belgian trippel are pretty educational. With many of the U.S. versions, you do taste the alcohol (HOTD isn't bad, though).
A lot of these beers would be great paired appropriately with food, but unfortunately you'll probably have to bring your own food to go this route. Also, you have to be over 21---it's kid-unfriendly. Still, it's worth a visit if you're interested in some of the world's best beers, and a lot cheaper than flying to Belgium.
(p.s. They do have German and British beers too, I just happen to prefer the Belgians. And I have no festival affiliations.)