I recently bought an iPad and decided to mount it in the car for big screen GPS and iTunes for music.
My effort is no better than a prototype, but I doubt I'll be able to improve it much - trying not to spend any money, just used parts I already had at home.
I used an aftermarket stereo mounting bracket, a bit of right angled metal, a wall speaker mount, small piece of thin MDF, and velcro (with one side attached to the back of my TPU iPad case). The speaker mount allows me to set the perfect position, and this brings the iPad closer to me, so I don't have to reach to change songs or whatever, but it's a bit in your face, so i may remove it. I've used wingnuts so I can easily remove the bracket if I need to.
I've temporarily mounted it in the top slot, and moved the stereo down but the stereo face plate is a different shape to the hole in the dash so it doesn't fit and looks ****. At least this way I can still access the stereo controls easily, but I don't need to as steering wheel controls will change volume and still switch to radio if I want.
And as you can see I haven't trimmed any bolts yet or painted any of it to make it blend in.
I'd love to do something like what these guys have done but I don't want to completely destroy the dash, and it would probably cost at least $500 (if not $1k including new dash parts) to pay someone else to mount it properly: