"I'm on Fire" is one of my favorites. Bruce was intrigued by slowing down Johnny Cash's "train" rhythm and had been thinking about lyrics. When the rest of the band was on break during a recording session, he and the drummer kind of flipped this on tape. Obviously, it got fleshed out a bit later, but the foundations were simple.
"Helter Skelter" is a great song that took on ugly overtones after being referenced by a maniac. Similarly, "I'm on Fire" can be looked at by overemphasizing the opening "Hey little girl, is your daddy home?" part. I think Springsteen is being poetic throughout the song and didn't mean it to be overly pervy.