The dream of a 90's wedding is alive in Portland! Oh yes, I'm inspired by Carrie Brownstein and Fred Armisen's sketch comedy show, Portlandia. Where would a Portlandian be likely to marry? These five sites came to mind:
The Woods
You go there to see your favorite bands, now you can get married in this Sellwood-area music venue that was once a funeral parlor. Can't get much more offbeat than that.
Holocene
Photo source: Cabel Sasser's blog, photo by Robert McNary

When your Double Down date decides to up the ante, don't worry -- you can get hitched in the club where you first met. Awwwww.
Secret Society Ballroom

I can't believe I'm even telling you about this site!
Bossanova Ballroom
If you need lots of space for lots of different amusements during your event, take a look at Bossanova Ballroom, which boasts an 11,000sqft. (750 person capacity) two level facility equipped with full kitchen, multiple bars, large performance stage, dressing rooms, billiard and game room.
Wonder Ballroom

One more music venue, The Wonder Ballroom is in NE Portland and holds 350 at capacity. A music venue bonus: most have ceiling rigging points and focusable lighting to amplify your decor.