Time Travel.
Ever sat there, thinking about past events and thinking - I wish I'd done that differently. That you wish you could go back, and change it? There are so many things I wish had never happened to me, and I could do just that.
However, I suppose part of growing up is to stop wishing you could change your past, and to instead learn from your mistakes.
Another one I'd love is teleportation. Someone halfway across the world that you feel really fond of? You just teleport, and hey, you're there. I'd like that.
Also, I'd totally love moustache growing powers.