Alternative spaces:
The Nepo House, Vignette, Season, Andralamusya
Every first Thursday of the month - art walk (pioneer square area) here are some galleries:
http://www.ggibsongallery.com/, http://www.platformgallery.com/, http://soilart.org/, http://www.4culture.org/arts/index.htm, http://jamesharrisgallery.com/, http://www.gregkucera.com/
and many more they are all within a walking distance.
Also, every 2nd Thursday of the month is the Capitol Hill art walk.
Frye Art Museum is full of events and you should check out their calendar.
Henry Art Gallery same.