I'm generating routable maps for Garmin devices supporting the gmapsupp.img, I wrote a script to bang out the areas I want and generate 'em. I'm working from planet.osm, and I use these two (Willamette Valley/Vancouver Metro) maps myself. For your convenience, I've also included the .osm files I started with.

I have to kick the script by hand, but I should be able to stay fairly up to date on it since I am eating my own dogfood and using OSM on my Garmin).

You can find the .img files and the originating .osm files at http://ursamundi.org/~baloo/osm/ (Please consider mirroring this if you are able to)

Update: I"ve given up on this since other people are clearly doing this better with less human intervention.