What substances I can use to clean the touch sensitive screens like iPhone, iPad?
I've found that the best substance is no substance. If you can grab some microfiber lens cloths online, you won't be disappointed. They absorb the finger oils well. I usually just breathe on my screen a little bit, then use circular swipes with a microfiber cloth.

If you are careful, any glass cleaner is fine. The reason this isn't recommended is due to the large percent of the market that would just blindly spray cleaner all over their device (causing a short), and the other percent of the market with non-glass screens. If you spray the cloth you are using, then wipe, it'll be fine.



Update 3/21:
My favorite method now is using Zeiss Pre-Moistened Lens Cloths Wipes. They're at Amazon and Sam's Club. I keep a box in the office and box at home.