This month, two mini tutorials were published on Elysiun on how to make a lightsabre in Blender.
The technique by Jason G is based on halo materials. By creating a finely subdivided mesh and applying a halo material of the right size he creates a convincing glow effect.
AniCator tries a different approach: he uses two halo spotlights with a low distance setting to get the glow effect.
I haven't tried AniCator's technique, but I would think that Jason's approach is easier to control and it will probably render faster as well. Still, it's cool to see how you can achieve the same effect in two radically different ways. If you have another way to create a lightsabre, don't be too shy to share it here!