My favorite (and I've tried just about all of them) is the Light Wedge
http://www.levenger.com/PAGETEMPLATE...98%7CLevel=2-3

It is different from other lights out there, in that you place it on your page (it is a flat piece of glass that is illuminated from within somehow) and it lights up your page, making for very little "extra" light -- great for reading at night in the car (while someone else is driving) or in bed while your partner sleeps.

I've had mine for several years, and have been very happy with it. It also comes in a smaller, lighter, paperback size, if that's your format of choice.