Japan's Ubiquitous Entertainment have developed a prototype device called ARider that allows cyclists to navigate via their iPhone 3GS using a heads up display. Of course, the whole setup seems a bit precarious for you and your precious phone.
First of all, using a HUD while cycling is inherently dangerous—but the display is retractable, so it's not like an eye is dedicated to it at all times. Plus, the iPhone is actually mounted unprotected on to the top of your helmet. Doesn't seem like a good idea to me, but ARider is in the prototype stage, so there is time to work out the kinks before it becomes an actual product—if it becomes an actual product. [zikkir via Core77 via Slashgear]