The Oregon Brewers Festival is just getting started as I write. I'm heading up to Portland this weekend and I would love to be at this event. There will be 72 breweries in attendance, which makes the festival the largest gathering of independent brewers in North America.
It's free to attend, but you have to buy a $3 souvenir mug and $1 tokens. Two tokens get you a half mug sample of a beer. Four tokens get you a full 14 oz. of beer. It's not cheap, but it's not much different than getting a non-happy-hour microbrew and it's an opportunity to sample many different beers in one weekend. Plus, there's easy MAX access so you don't need to bother with driving.
One of the contributors to BlueOregon has a guide to some good beers at the fest.