If you're looking for an eReader with a backlit display, which can greatly increase when and where you can use the device, two popular options are the Nook GlowLight 4e and Kindle Paperwhite.
Meanwhile, Nook has a more limited range of e-readers. The Kindle Paperwhite offers a larger screen with adaptive front light ...
The new NOOK is cheap, and has more capabilities than the similarly priced Kindle Paperwhite, due to its status as a tablet, but Amazon's tablets are selling for far less this week.