I like the ebook-Lite from Target which is similar to the Kandle. It was ~$20. I like how it aims a larger amount of light on the screen. It has a spring clip that adjusts to different thicknesses so it works with several ereader brands and cover combos. It also has hi & lo settings. I use it with my Sonys and my Kindle.
http://capstoneindustries.com/ebook•lite.aspx
I also have a mini clip-on Book Owl light with a flexi-neck that I got in the check-out lane at Borders. It was ~ $10. It focuses the light on a smaller area so I have to adjust it more often. However, it's convenient for carrying in my purse.
http://www.borders.com/online/store/...=9781931931472