Hi

Andrews Areospace has an interesting discussion paper on interstellar options...

Andrews Publications

...it's a javascript menu so I can't give the direct link, but the titles are clear. All their papers are interesting, just not directly related. Interstellar Transportation is the relevant paper.

Jordin Kare also did a NIAC study on the laser-bomblet drive which is worth a good read. Some other interesting NIAC studies are Zubrin's magnetic sail paper, Christensen's Interstellar Solar Sail paper, and Landis' Laser Sail paper.

These are just a few of the concepts for interstellar travel. Lasers and/or neutral particle beams might not be the best options either. Jordan Maclay and Robert Forward have described a quantum photon drive that might allow a continual multi-gee drive to arbitary time-dilation factors. Eventually the Cosmic Microwave background is the limiting factor - when the light-drag from it is equal to the photons pushing you forward that's the limit velocity. A relativistic version of "Doc Smith's" speed-limit on inertialess drives.

Adam