My wife just picked up the Capstone E-book lite for me. I like it very much. I first read it blogged about here: http://www.simplyparticular.com/2010...ption-for.html
We could only find it at target, but I just googled and it is being sold on ebay for less than half what we paid for it.
It stretches all the way across the K3 top, so it provides a nice sheet of light, about page width. As is the case with all lights that I have used, it takes some fiddling to get the light just right for reading in your favorite position. The light rotates about two axis, so there is quite a bit of adjustment possible.
What I wondered before we picked it up was how well it would move to the thinner device. The piece that holds it to your reader actually pulls out and has click-stops, so you just click it into the right thickness and it slides right on.
I like it a lot. I am not sure why there are no good internet channels other than e-bay selling it yet. Possibly an exclusivity with Target.