I voted some powers instantly like super strength, and he continues to develop others in puberty with flight as a big culmination somewhere in his early 20s ideally. I think the movies and Smallville have done a good job showing it.
I also love the idea that he keeps pushing himself further as he needs to. Like Jor-El said in Man of Steel, "You've grown stronger here than I ever could have imagined. The only way to know how strong, is to keep testing your limits."
I was also just thinking, could Superman become even more powerful and develop new powers if he lived near a star like Sirius, which is supposed to be a lot bigger and brighter than the Sun?