A while ago TFN ran a lightsabre competition to see if any method for rotoscoping lightsabres was preferred. It turned out that the top three winning methods where created using a variation on one of the tutorials below.

These tutorials take the form of quicktime visual tutorials complete with step-by-step commentary (make sure you have speakers!) Ideally download the files, and view them on your desktop. Remember to Right/Alt Click and save them to your desktop, as you will probably use them more than once.

Lightsabre glows in Adobe After Effects
Right Click image to begin downloading the 11.2MB file.
Click here for additional notes on this tutorial method.

Lightsabre glows in Adobe Photoshop
Right Click image to begin downloading the 5.6MB file.
Click here for additional notes on this tutorial method.

Related Links:
PostProduction Tutorials