I've published a spreadsheet here that has the put-in and take-out coordinates of some of the class II, III, and IV runs that are popular among Seattle boaters.

There are a couple of ways to get this data into your car GPS. I can only talk about the Garmin world, but there are undoubtedly similar tools to use in the non-Garmin world.

I'm going to briefly write how to do this but I can't provide tech support for these tools. The easiest way to use this data would be to turn the data into a .gpx file and upload it to your Garmin device using a product like Mapsource (download from Garmin). Turning the data into a .gpx file is easy using a website like gpsvisualizer. Then, take the .gpx file generated on gpsvisualizer and upload it to the Garmin. All of the put-in/take-outs are now "favorites" a.k.a. waypoints.

The other way to upload the data into your Garmin is to use Garmin's POI (point of interest) Loader (also download from Garmin). Put all your POI files (including this one) in a folder and point the POI Loader at the folder (and plug in your Garmin to the computer). This will blast this file to the Garmin. These points of interest will show up under "Points of Interest" or "Extras" depending on your model. If you go down this route, you might want to poke around the web for other POI files you can download. Two particularly useful ones are traffic light cameras and speed cameras.

There is a subtle difference between having these points show up as Favorites or Extras. Most devices can handle a small number of Favorites (say 1000) but virtually an unlimited number of points of interest. The other difference is that if your Garmin can do multi-destination routing, the destinations in that route must be "Favorites" not "Extras"

I've opened up the file to allow for editing by anyone that has the link to the file. So, feel free to correct errors or add put-ins and take-outs. An easy gmaps mashup to do this is here