Two different proposals by three different physicists have come to light recently.
New York University physicist Jia Liu has suggested using dark matter in a manner like a jet engine in order propellel a future spacecraft to other star systems.
Then from Kansas State University, Louis Crane, and Shawn Westmoreland; believe that miniature black holes would be a better power source.
And so far, the telegraph article points out, there doesn't seem to be anything in the present understanding of physics that would rule either of these proposals out. So states New Scientist.
The black hole proposal would have a huge parabolic reflector behind it, and then putting a small black hole at its focus. The "Hawking radiation" given off by the black hole as it slowly converts its mass into energy would push the spacecraft to near light speed within a few decades. This would bring Proxima Centauri at 4.2 light years away - in more reasonable reach of humanity.
As far as Mr. Liu's proposal of using dark matter, he is suggesting a spacecraft have a large intake at the front end with which to scoop up dark matter particles. If theory holds up, then the neutralinos particles would annihilate each other on contact, they could be forced into a bax at the back of the spacecraft which would fire the energy rearwards like a jet engine. The faster the ship travels, the more neutralinos it would pick up, and the faster it would accelerate. Mr. Liu thinks that the ship could reach near-light speed in just a matter of days.
Of course, dark matter brings up other problems. It would need densely area is 26,000 light years away in the center of our Milky Way galaxy. Also, neutralinos barely interact with ordinary matter. Holding that dark matter would require new - and currently unknown material science.
And as any true Star Trek fan can tell you, Romulan use artifical quantum singularities to power their huge D'deridex - class warbirds.
Telegraph.co.uk. "Future spaceships powered by black holes and dark matter" By Tom Chivers November 26, 2009. (http://www.telegraph.co.uk/science/space/6662603/Future-spaceships-powered-by-black-holes-and-dark-matter.html).
Picture of Romulan Warbird from Star Trek the Next Generation (http://www.ex-astris-scientia.org/scans/romulans1.htm)