Well, if you're a Stephen King fan I'd suggest
UR, a Stephen King novella about a special Pink Kindle (K2) that has a mysterious "UR Function" on it.
My first e-reader was several years ago and was MobiPocket Reader on a Palm Zire 71. For my very first e-book I chose
I, Robot by Isaac Asimov which I had read many, many years previously as a paperback. Of course I didn't buy it at Amazon because the Kindle didn't exist then.