I realize this is an old thread, but nobody mentioned my favorite light, the Kandle:
http://www.amazon.com/Kandle-Ozeri-D.../dp/B0031116K8
It was originally designed for the Kindle, but it works great on both my classic nook and my nook touch. It's intended to be clipped directly to the device, with or without a case, which it does just fine on my nooks without depressing the power button on either. It casts an even, bright light far superior to every other book light I've used, including the lightwedge case I had for my old Sony 505.