(greped from Jay Lake's link salad)
Okay, here's a Science Fictional concept, the spaceship is the engine. I'll let you read the whole thing (if you're interested in such things) and except to say, now that is a concept. Of course, at least for me, we're still talking generational arks here (proposed speed would be on the order of 0.1C, so even a short trip to a nearby star would take centuries) as I don't believe in some of the outside "human life expansion" theories (which, IMHO, are based on the mistaken cultural belief than humans are not animals).
Now, there are other ideas for starship propulsion that have greater capacity for speed, although their energy requirements are astronomically high (as they involve the manipulation of space density). This idea, on the other hand, use technology that is within actual near time reach (like within 50 years, except for the human life extension stuff, which, like I said, I don't think will really ever happen).