Having spent far too much time and money trying to mount an iPad onto the handlebars of my bike, I know all about fastenings both simple and complex. And I also know when to quit with the DIY and just drop some cash.
The Satechi Bikemate Slim 3 isn't big enough for the iPad, but it will fit iPhones both tall and fat, and its mounting is both simple and easy to use.
The Bikemate Sim 3 is essentially a rain-resisting, dust-shrugging plastic bag for the iPhone which clips to the handlebars of a bike or motorbike. The mount attaches using an oversized cable-tie and the padded bag clips into place, kind of like a flashgun clips to the top of a camera.
And that's almost it. There's an opening at the bottom so you can attach a dock cable without removing the iPhone (handy for hub-powered or solar chargers), and with the iPhone 5 you can also thread the headphone cable through the same hole, thanks to its bottom-exiting jack.
The plastic, like most plastic (including the humble ziploc bag) will transmit your finger-power through to the screen within, letting you use it safely even as you pour sweat all over it.
Finally, there's the price: a decidedly practical $25. This, combined with the non-tempting (for thieves) mount, and the easy, foldaway (and pocketable) nature of the bag itself make it pretty ideal for most iPhone/bike related uses.