hackThisSite.org

Well, this site is one of the few sites which offers pretty impressive tutorials and techniques to nourish hacking skills.
however, This site doesn't make you a hacker :p
It only gives ideas about how the hackers work.
And if you don't know how the hacking works, you can't protect yourself from hacking, right?
As philosophy says, "Know your enemy"
Know how hacking works, for your own safety