I can really relate to this. There are many aspects of programming that contribute, I think: you are creating something, ususally something useful to others, which you are (often) in complete control of, and (in the words of Fred Brooks):

"The delight of working in such a tractable medium. The programmer, like the poet, works only slightly removed from pure thought-stuff. He builds his castles in the air, from air, creating by exertion of imagination."

I love that quote! More here: http://henrikwarne.com/2012/06/02/why-i-love-coding/