I'm off to the Low Countries in September so will be taking the GPS as well as a Michelin map. I downloaded this last night and after downloading a couple of extra Garmin plug ins got it to run OK on the Mac. I've not tried to dump it onto the GPS yet though. Looks rather pretty. There is also a version for Germany, but that's a .exe , so presumably Windows only.
http://sites.google.com/site/openfietsmap/
