At the moment, the well-known governmental space agencies put no serious funding behind interstellar propulsion research. In the past, some government-funded programs existed such as Nasa's Breakthough Physics Project or the US Air force's Orion spacecraft design.
Most work on interstellar space travel now is actually been done by interested scientists and engineers as side-projects in their free time. Of course, without funding this work does not go past the design phase. Nevertheless, several credible designs have been proposed and are just waiting for further development and testing. Also, a worldwide community is growing, consisting of scientists trying to get interstellar propulsion research accepted as a mainstream science that has every right to be taken and funded seriously.
Here are some links to a growing community:
Dutch site about visionary work in general:
For those who think one planet is enough for humanity to survive for a long time to come:
Evacuate Earth (National Geographic film about building a starship within 75 years, when an approaching neutron star is found heading for Earth.)
Our Prezi space projects