The best clip-on light I've come across is my gf's. Believe she got it from Costco. Very similar to this Ritelite from Amazon but has 4 LEDs instead of 5:
http://www.amazon.com/Ritelite-LPL79...3481729&sr=1-2
Problem is, I can't find the 4-LED version anywhere! (And no Costco nearby.) But the light is amazingly even on the screen with no glare. Has blue glowing spots on the back behind the LEDs. The gooseneck also detaches and plugs into a usb port, or use it with the 3-AAA battery clip-on base. This light is much better than any other I've tried, incl. the 'candy-bar' z-light and the regular Mighty Bright. The 5-LED version will probably work great as well, but the 4-LED version should be fine for any ebook device. Does anyone know where to find the 4-LED version (online)?.