I just took my family up to Snoqualmie falls, with friends, and this is a great spot for rafting and kayaking.

We hiked down from the top 1/2 mile, and at the bottom it's awesome. The falls from Snoqualmie fall from what looks like 250 feet, and just roar into the river at the bottom. While we were hanging out on the rocks, a couple kayakers were paddling around the white water, from where the falls were crashing into the river. I wanted to see if they were going to try to go into the falls itself, but that probably would have been deadly.

Anyway, these guys flipped their kayaks around, and headed down river. About a hundred yards away was some white water and boulders, and these guy had no problems there. After that, a number of people were hopping in with tubes and rafts, etc to float the river. I don't know how far down it goes, but this looks like a river you could probably float for a few hours.