Depends what style music, day of the week, food or libation preference, and which part of town.
I love a LOT of music and go often to Duffs Garage, the Laurelthirst Public House, Halibuts, the Mock Crest Tavern. Slim's Bar in St Johns, the Muddy Rudder, Biddy's, Jimmy Mak's, the White Eagle, Rock Creek Tavern, and more.
The first 2 and Biddys have Happy Hour Music most days, so a Good place to start. Some daily listings are in the online Willamette Week. For Blues check CascadeBlues.org