I planned a trip a few weeks ago and used Google Maps to lay everything out. There ended up being about 10 other bikes planning to go, several of whom had GPS units on their bikes. I think the prevalent model was the Zumo (Garmin). I worked extensively with one of the guys to export the routes to .kml files from Google Maps, run them through GPS Visualizer, then the other guys were able to create Garmin import files (.gpx) for the GPS using Basecamp. My understanding was that the generated .gpx files required a fair amount of "tweaking" in order to get to usable GPS files. The process wasn't seamless, and I don't have Basecamp, but I could write up a tutorial on how to do the first part. Personally, I use my Android phone for creating and following moderately complicated routes. The Android integration with Google Maps is fantastic. Once I've saved a route to "My Maps" on my desktop (just have to be careful not to check the "avoid highways" selection or else the Save to My Maps option goes away), I can open the same map on my phone and just follow the blue line. The route doesn't come with turn-by-turn directions or audio (I'm trying to learn Android programming to come up with a "fix" for this), but a quick glance down at the phone while I'm stopped at intersections is enough to keep me on-track.
