Interested in hearing theories about what exactly Touma's power is, what potential uses it has, the extent of the power, the nature of the power, etc.
We all know that it negates magic and esper abilities. It also even negates his own luck, which makes you wonder what exactly 'luck' is... is it magic?
Also, is it important to put emphasis on the word 'negates'? I mean, I don't think we've seen it explained as something that nullifies. 'Negates' gives a notion that his power simply removes something from existance, while 'nullifies' gives the notion that it's a power that applies the same type of force as of that in which it is acting upon, hence the spell or whatever becomes ineffective.
So what are the extent of his powers? Does simply grabbing someone with his hand prevent that person from using his powers or casting spells? We saw the teleportation chick and couldn't teleport Touma while grabbing him. Important to notice that she didn't grab Touma's right hand, so this example might not be representative of possible uses for Touma's powers, but it's a starting point. We also remember when Index was dying and needed to be revived that Touma was forced to wait outside since his pressence alone would affect the spell... something to consider.
Also, would a projectile that has been shot magically harm his hand? For example, when Mikoto shoots a coin using electricity towards him, if he had put his hand up would it had pierced it? For some reason I think that if he were to touch the coin, the coin would lose all it's momentum... since the force that theoretically was driving it forward (the magic/abilities) is negated, so it might return to its original stationary state. Might not be probable, but I think it would be quite cool that way.
We saw a preview of it with the alchemist, how he negated the magic bullets and the falling car. But then again, they were just that... magic.
I think that's all I have at the moment, feel free to add, theorize, challenge.