Crystal and I have been reading Kindle books recently and have found many good deals on them.
Monergism is offering a good collection for free here.
Also, Amazon is constantly giving away free books here.
Even if you don't own a Kindle, it is still a great way to get and read books. We read many on our computers and even on our iphones. (Crystal often reads me books as we travel in the car and the iphone is great for this. It doesn't necessitate a flashlight or dome light.)
My reasons involve mostly getting to read the classics without the moldy book smell (I know, I know, that is probably all part of the experience... You can keep your experience and your allergies too.)