The Hunger Games on a 1st gen iPod Touch.
I had not paid much attention to ebooks other than to scoff at the price of the original Kindle, but we went on vacation & I finished my paper book early, so downloaded THG for the Kindle app. Thought it was handy for vacation but still didn't really see a personal need for an e-reader. Little did I know my husband knows me better than I know myself. He gave me a Nook Color for Christmas a year later & I haven't looked back since
Aside from packing lighter, it has an added bonus - my family & friends know how much I love it, so where I had been relying heavily on library borrows before, I now almost always have a B&N gift card on hand - woohoo!