I am going to post from a electronic music point of view cuz thats what I like
Seattle, Washington
Best club: The Showbox at the Market or the Showbox at Sodo, but they mainly have non-electronic actc. They are bringing Bassnectar, Mark Farina, Paul Van Dyk, and some other acts over the next three months. Chop Suey and Neumo's have similar lineups, but are smaller.
21+ Clubs that have techno somewhat regularly in combo with hiphop(usually one room of each, and the techno can be house, trance, or drum and bass)
The Last Supper Club
Trinity
The Copper Cart Cafe
Heaven
See sound lounge
Clubs that often have 18+ shows: (various techno, lots of hardcore/happycore/hardstyle)
Motor
King Cat
Jumbo
Smaller Clubs that are in Bars:
Contour (Breakbeats on sundays, dubstep on fridays)
Temple billiards (Drum and bass on saturdays)
Baltic (Drum and bass tuesdays)
Re-bar (House on sundays)
Waid's (psytrance once a month)
Noc noc (darkwave/goth, has some techno once in a while)
Lo-Fi
Nectar - don't do much electronic any more
Tost - don't do much electronic any more
Undergroundish club/venues with a great vibe (in my opinion):
Electric tea garden
Church of bass
Space
Little red studio
see
www.nwtekno.org for more info on seattle and portland shows, they have all the electronic music listings.
WaMu theatre sometimes has giant rave shows (i.e. Daft Punk played there, and they are bringing Tiesto there soon.... who apparently is playing some dubstep now?!?! wtf?)
There is a boat called the Islander that has regular electronic music parties on it (about once a month, go from 8-2)
Overall, my favorite club right now is probably Contour. One of my faves used to be Element, but it closed down and got renovated, and is now some stupid hiphop club i think.
Maybe someone else can fill in the portland info?