Already bought a book and don't want to buy it again to read on a portable device (like the iPad)? Consider transforming an old digital camera into a DIY digital scanner for less than $US20.
Using guidance from DIY site Instructables and a few metal rods, you'll need to create a frame in which to hold the book and/or document. To scan the book or document, the picture needs to be clear while the pages are flat. This contraption uses the rectangular frame to press the open book flat, and the corners are connected by rods to the camera, making sure the images are steady.
After taking the picture, and you'll most likely want to clean them up in an image-editing software, paste them into Word, turn it into a PDF, or run them through an OCR (optical character recognition) program to make them searchable documents. It's a completely different way to scan your documents than previously mentioned document-processing service Qipit, but if you've got some time and want a digital version of your analogue books, it might be worth a try. If you do scan to PDF, you may still want to consider converting your book to ePub format to make it more ereader friendly.
New & Improved Portable, Paperless, Digital Copy Machine [Instructables via Wired]