Although bike-mounted GPS devices are fairly common in Tokyo, a new contraption that uses the iPhone 3GS takes the concept to a new level. Created by Ubiquitous Entertainment, the ARider system combines a head-mounted display, a bike helmet and the iPhone 3GS to give riders a real-time map that uses the iPhone's compass to adjust the map to your current orientation.
The set-up can also be used to make hands-free calls and connect to Twitter using TwitBird Pro. Aside from the relief this will give bike messengers, this could also prove to be a very interesting tool for GPS-enabled life-casting. You can see video of the ARider system in action here.