Expand minds. Not just add new knowledge but also help people to change their mental models of the world around them; to think differently and be able to conceptualize new ideas. Experimentation, reasoning and analytical skills, and critical thinking are force multipliers for technologists. It is a primary responsibility of leadership to change what people are capable of, to make their organizations about more than just turning the handle the same way.
Set purpose. Everyone needs a purpose, and I mean a higher purpose, which transcends job description. The reason you're really here gives you the confidence to make better decisions. For example my guys aren't just here to write some code, or hack away at the Linux kernel, they're here to change the way people build web travel apps. The better you get at describing what that means and why it matters for customers the more independent and powerful your team can become. It is a primary responsibility of leadership to favor being highly descriptive over of being highly prescriptive, because it creates the space for teams to contribute at another whole level, not just follow orders, yet still be totally on strategy.
Hire up. Any great human endeavor is bigger than all of us and can only be accomplished by valuing a smart, talented team over valuing being the smartest, most talented person in the org. It is a primary responsibility of leadership to constantly raise the bar and bring in people than make you look dumb.