An Amazon Kindle, and a subscription to Audible.com.
When I bought a Kindle, I really did so on a whim (they're cheap!), but they're actually incredibly awesome devices. Ever since I've gotten one, I've read far more books, learned a lot, and have greatly improved my personal satisfaction. I've always been the sort of person who feels 'guilty' when I don't read frequently, and having a Kindle around has really solved that problem for me. It makes it very easy to swipe, read a few pages, and set back down (while code is compiling, whatever).
The Audible.com subscription has also been really amazing. If you're not aware, Audible is an Amazon company that sells audiobooks. You can listen to them on your mobile device (Android, iOS, etc.), and it's a great companion for running errands, commuting, doing chores, or working out (unless you're lifting weights, in which case you may want some real music >:)).
Audible has essentially helped me read through an extra ~40 books last year, all of which were really educational / helpful.
Earlier this month I decided that I'd finally get one... so, I thought I'd get the DX (because it's large, and I figured since I'd be reading normal PDF's made for standard sized papers, it'd be my best bet) -- but, it seems Amazon stopped making them. Which is a pity, because it's everything I'd wanted: e-ink display, and large.
I still read technical books in paper, but I read business / personal development books primarily on the kindle.
[1] http://www.amazon.com/Motorola-S305-Bluetooth-Headset-Microp...
I take the train every day and using an iPad 2 to read is really inconvenient and invites theft. The Kindle fits in my coat pocket, is a delight to read with (sitting or standing), and no one wants to jump you for an e-reader.
Kind of like this: http://www.amazon.com/Automatic-Wire-Stripper-with-Cutter/dp...