You already use your phone in your car to perform a whole load of functions. Why not use it in your bicycle, too? That's exactly what you can do with the Handleband.
A universal bike mount designed to dock your phone onto the handlebars, it offers a quick way to turn your smartphone into a multi-purpose bike computer. At the least, it lets you use your phone easily while you're on the bike, giving you full access to the display all while your hands stay on the handlebars. That way, you can watch funny YouTube videos while commuting to work, likely leading to your accidental death after crashing into a truck coming out of a corner that you failed to see because that darn cat is just so funny. Or something like that.
Morbid possibilities aside, the Handleband is a simple mounting tool that straps onto any cylindrical surface with a diameter of between 1 and 1.5 inches. Construction is high-strength silicone, allowing it to stretch to fit most any type of smartphone, with an aluminum spline to give it stability. According to the product page, it should handle most phones even with their cases on (so you can dress it up in a waterproof case for use in the rain), although it might not be able to accommodate larger ones with a case on (e.g. Samsung Galaxy S3).
With the phone on your handlebars, you can use it the same way you'd use a phone in the car -- turn-by-turn navigation, hands-free calls, and whatever other app you like to run while on the road. You can also mount your phone to use the rear LED as a bike light or even the camera to film the road ahead. While it's stable when secured, it's also easy to remove, so you can quickly get it off when you need to leave the bike outside.
The Handleband is currently collecting funding on Kickstarter. Pledges to reserve one starts at $25.