The trouble with fast growing plants is they keep on growing, mostly, so I'd concur with Teresa's recommendation of Bamboo for fairly rapid cover, but also concur that you'd need a root rhizome barrier, not just to protect next door, but to stop the bamboo appearing 10 to 20 feet away in the middle of your garden.
I was wondering about Berberis darwinii, but that usually only reaches about 8 feet and isn't fast growing. Seattle seems to be in Zone 8/8b, so Pyracantha could be another option - it's not a slow grower and can usually be bought at a height of 1-2 feet for a reasonable price, well, in the UK anyway, can't see why it'd be different there. Both are evergreen and produce berries, but both are prickly - thorns on Pyracantha, prickles on the leaves of the Berberis.