Touch Screens in the field of enabling disabled people are no new thing. Brilliant Computing, formed by Nick Pronger and Rod Boyes in 1986 were pioneers in this field. They published many games and activities, many aimed at some of the most severely disabled people in the UK, enabled using BBC Micro's with Microvitec touch screens and other alternative access methods. These days, with it possible to buy iPads and PCs with touch screens from standard computer shops, life is easier still.
Inclusive Technology stock one of the nicest PC touch screens I've seen in their One Touch package. They back this up with some lovely free on-line activities in Help Kidz Learn. Latest is the doodle with colour activity Hidden Grid.
This reminds me of Llamasoft's wonderful light-synthesisers of years gone by, Psychedelia and Colour Space. I used to set these up for people in a Sensory Room on big TV with a mirror box to boost the effect, controlled using switches or a big floppy joystick.
I'm rambling a bit here I realise. Whilst researching a bit more about pioneers of accessible gaming, I stumbled upon another really nice on-line touch-screen compatible activity page: Philip Whittaker's Moving Targets page. Another great tracking and cause and effect area.