The Kindle Keyboard from several years ago offered it - it was not that good from what I recall, though did work if all you wanted to do was to read a mumsnet thread (have Mumsnet options set to display the entire thread in one go, rather than in pages).
Doctrine, I wanted to be sure I could swap between book and M internet, and also it would save my smartphone battery!
The Nook sounds interesting. Is the Glow's light okay/comfortable, though? DH has a kindle with reading light, and I've also tried reading lights with proper books in the past: that small circle of light is not great, either.