What's the best bet for a fundamentally new energy source from physics?

Antimatter doesn't look particularly promising. There just isn't enough of it, anywhere, as far as we can tell. Controlled nuclear fusion looks like a problem of not being able to have your cake and eat it too -- we can't get commercially viable levels of energy production from nuclear fusion without creating, effectively, a dangerous nuclear bomb. Antigravity won't be practical unless gravitons exist, and we don't know that they do. So, what really exciting fundamentally new sources of energy does physics present to us on the horizon? Anything?