Hm, if I were a super-hero, I'd have the power of... MONEY! (Half-jokingly)
Sadly there's not much you can do in the world without money, and a lot of people could benefit from large donations to charities like the Red Cross or the Salvation Army.
But if you're talking about a strictly "Super" super power... I'd choose to be able to increase my focus to the point where I could slow down time. Flying WOULD be a better way to get around, but if I can concentrate on things, I can already do some pretty cool stuff; I just need more time to get em done, and not lose interest in it. x)