You probably want to look at something like the Garmin Oregon or Colorado series. These are general purpose handheld GPSes, but have handlebar and car mounts available, and can be loaded with City Navigator maps for full road navigation.
I believe they will even integrate with the Garmin heart rate and cadence sensors so other than size and weight (and power meter integration), I'm not sure what the Edge 605/705 offers over them. Maybe some of the more bike-specific functions like the aforementioned power, as well as some of the features related to courses and auto-laps, etc?
I used to use a GPSMAP 76csx in my car/bike before I got a nuvi for the car and and Edge for the bike. The nuvi has a bigger, brighter display but the 76CSx has more features (the ones I miss the most are saved tracks, and the heading arrow on the map screen).
Last edited by Metaluna; 04-23-10 at 09:56 AM.