NOAA: NW River and Weather Forecast: How's our river trending? Provides flood stage, velocity and general weather forecast.
USGS: This site is a great resource for finding water temps and discharge rates. Here's a quick link to the Willamette at Portland location. This is the main Oregon map for more links to specific data sites around the state.
Wind-Speed.com is a great, easy forecast site for the Gorge (Rooster Rock to Roosevelt).
WindOnTheWater.com
Wind speed readings in a Google Map updated in real-time. Also has WAP support.
NWKite has a whole list of forecasting links (including the coast) that you can wade through.