I've always kept my phone (or water bottle) there since I've had the car like others. I haven't actually done any research in the products I would use with the appropriate size, but recently got a new phone that supports wireless charging and have thought about "converting" the cup holder into a wireless charging station. Since there is a 12V outlet near the cup holder in the footwell, I could wire a USB from there to a Qi wireless charging pad that I will have secured in the cup holder. Essentially, am still using it to hold my phone but it now serves to charge it as well.
Something small like this:
http://www.amazon.com/PowerBotŪ-Comp...i+charging+pad