A very easy tut. I used Photoshop CS2. This was supposed to be a tut for Gimp so all credit goes to Martin.
 
1. Use a black brush or make a black and white linear gradient (thanks to uttaresh) to draw over white background. Cover about a half of your image. Go to Filter>Blur>Gaussian Blur and put the radius on like 50.
 

 
2. Go to Filter>Render>Diffrence Clouds. Your picture should look something like this now:
 

 
3. Press Ctrl+i. Press Ctrl+l and move the darkest triangle to the right until u like how your lightning bolt looks.
 

 
4. Press Ctrl+U and click on the colorize square in the bottom right corner of the screen. Adjust The color to your liking.  
 
Here is the result:
 

---------------

Nice and simple, but I already knew this one, too. One of the first ever tutorials I learned. Here's a very basic manip I made back when I'd just started PS:
 
http://starwars.yahoo.com/photos/t [...] d&ue_dpln=
 
By the way, it helps if you use a black-white linear gradient instead of using the brush tool. Brings more of a natural, continuous effect.

---------------
Glomping the internet populace.

One forum at a time.

nice pic. here is another one i made
 

---------------

That looks nice, as if the Emperor is torturing it for not turning to the Dark Side.

---------------
Glomping the internet populace.

One forum at a time.

(off-topic: you really are a fan of starwars aren't you?)
(off-topic: Ithink its is the other way around - the car got powers from the dark side like anakin and got cool new armor, and when ani threw the sith lord down the ... whatever the thing is called... he got shocked... did I say too much?)

---------------

Oh, you mean when Darth Vader throws the Emperor down the shaft to the power core? Yeah ... it does look like that.
 
I'm an ex-Star Wars fan, till the Phantom Menace. Did not like II or III. Oh, and the video games! I loved SW video games till they ruined them. Knights of the Old Republic, Republic Commando, Battlefront, Galactic Battlegrounds, Episode I Racer ... they were just wow!

---------------
Glomping the internet populace.

One forum at a time.

I liked Star Wars the Force Unleashed, but I quit playing it... I was wasting too much time

---------------