Don't think this has been mentioned on here before.
Requirements - HW computer connected to network which has wifi, iPad, a bit of time to fiddle
There's an app in the iPad appstore called TouchOSC. It is basically a similar concept to the Novation Launchpad in that it send MIDI data based on what you press, in this case wirelessly to your HW computer using the built in Apple Network Midi driver. The manual says there is a windows driver too (untested)
There is an accompanying program for OSX or Windows which is an editor to allow you to create your own layouts of switches, faders, LEDs etc.
With a bit of effort one can create a layout with coloured toggle buttons for stops, and combinations, and lay them out as you wish, in my case mimicing the stops on a console with a load of general pistons in the middle. The designer software makes it very easy to send the layout to the iPad. Then the last step is setting up the Network midi driver and programming HW (using auto-detect) to respond to the MIDI messages it sends. The nice thing is that HW can also illuminate the buttons in TouchOSC on the iPad, and if you use the Master general pistons it will illuminate the last one you pressed. (I haven't got reversible pistons working yet before someone asks!)
If you know a tiny bit about MIDI and want to use the iPad as a Hauptwerk controller this is worth a try. I have done an a TouchOSC layout for the Haverhill mini console and after a while stopped looking at the real HW screen as I grew to trust the iPad, and having never had a touchscreen quite enjoyed this!
Here's a link to the website http://hexler.net/