eForCity Leather Case for Barnes and Noble Nook Simple Touch with GlowLight , Blue
I have tried multiple covers out and this one is the best of the ones tried.  The sizing is perfect for the Nook (unlike other covers), the magnet clasp has enough strength to easily keep it closed (unlike other covers), the cover feels solid, the buttons are easily accessible (unlike other covers), and there is a pocket inside to hold additional paper.  Very pleased with this.