The Horse Brass Pub is one of the best beer bars.
The Green Dragon is also fantastic, as is Bailey's Tap Room.
Rogue, Deschutes, Widmer, and Full Sail all have taprooms if you want some good stuff from the larger breweries.
Cascade Barrel House is the place to go for locally made sour beers.
Honestly, there's so much good beer in Portland, you can get a great tap selection in some of the numerous strip clubs. The Acropolis possibly has the most taps.