I've been using a case/light from a Sony Reader Pocket Edition. It's exactly the right height for the nook, although the right-buttons do stick out a little.
The case is sturdy, the lighting is excellent. I find it funny that the three-position switch suggests dimmer, but it actually seems to switch from off to on to - well - on!
Two strips of Velcro (or double-sided mounting tape) will hold the nook snugly in place, and afford protection against bumps and short drops.