I saw a product at Aerostich (can't find it now) that was an LED light for your panniers. They basically took an LED headlamp, removed the strap and affixed it into a pannier. I decided to make something up for myself.
I went to Academy Sports and bought two
Cyclops Atom headlamps for less than $7 each (batteries included). I also bought some Super Lock fastener from Radio Shack. The Super Lock is adhesive backed heavy duty velcro like fastener.
I removed the head band from the lights and attached Super Lock to the back. I attached a piece to the inside of the pannier too. The Atom light pivots 90 degrees.
It was hard to get a good picture with the interior lit but it works pretty well.
The total cost was less than $20.