This item from WIRED introduces a book more authoritative and up to date than the research I mentioned surveying for NASA. The put the lessons in the book Frontiers of Propulsion Science into a really condensed condensed version: Antimatter warp drive is not going to make it. Traversable wormholes are, eventually, maybe, a possibility. Travel via antigravity and "free energy" are out - there's no evidence either works on even the smallest scale.
Definitely a book I need to read.