If you haven't yet made the jump to ebooks, I'd like to take a few minutes to explain why you should. Ebooks, or electronic books, are digital copies of books that can be read on a variety of devices. You can purchase ebooks through companies like Amazon, Apple, Barnes and Noble, and Google, and there are also many free ebooks that you can download as well.
Ebooks give you the ability to literally carry thousands of books with you on one device. You can also instantly purchase and download from a library of over 800,000 books. The combination of instant access and a digital library that can be carried anywhere gives ebooks a distinct advantage over traditional paper books. And e-ink ebook readers provide a technology that imitates the look of paper on an electronic device. Its very simple to purchase a new book right from the device. No computer needed.
Another advantage of ebooks is that you can access your library from multiple devices. You could start reading on your kindle e-ink reader, read a few pages later on your iphone, read a few more pages on your laptop, and then pick back up on your ereader later in the day. Kindle keeps all of the devices synced up so that your device always starts on the last page where you left off.
I personally prefer the kindle system because they have a huge selection of books and you can access your library on many different devices. For pure reading, the kindle e-ink reader is the best experience because its the closest to reading on paper. There is no backlit lcd so it seems to be easier on the eyes for extended reading sessions. The only disadvantage to this device is that you do need a booklight for reading in the dark.
However, because I am so busy and always on the go, I find myself reading more and more on my kindle iphone app. I always have my phone with me, and the iphone has a very high quality retina display that produces extremely clear text. It was a little small at first, but text size is adjustable. I've gotten so used to it that I frequently read entire books on my iphone.
If you want a multi-purpose e-reader, you will want to look at either the iPad, Amazon Kindle Fire (affiliate link), or a barnes and noble Nook Tablet. These devices are great for reading, but they also are full-fledged multi-media devices that allow you to watch movies, listen to music, play games, and surf the web.
The Kindle Fire and Nook Tablet, are low-prices at $199 and $250 respectively. They are a great bargain. However, they are smaller than the ipad at 7" and they do not have the massive app store that the ipad has for additional functionality. The ipad has a 9.7" display, and has its own ibooks bookstore as well as specific apps that give you access to the kindle and barnes and noble bookstore.
The cheapest entry point is the new $79 kindle with special offers (affiliate link). Its an e-ink reader that gives you access to the kindle bookstore for a great price. The special offers reduce the price by adding advertising to the kindle screensaver when you are not reading, so it shouldn't be intrusive. Plus, you can pay additional money and remove the ads at any time.
Anyway you go, these are all very good devices and should get you up and reading in no time. After a while, you may wonder if you'll ever buy a paper book again.