You can find a load of free downloads, but the rest you'll have to pay for. I'm a bookworm, so I received one as a prezzie a few years ago. I've used it a handful of times. I do not enjoy reading a book on a kindle, but I do like some of the educational literature I download (languages, etc). Reading a book on a handheld device does not give me the same fulfilment as flicking through real paper pages.
Play around with one first, or ask to borrow someones for a few days. 49 quid is cheap, but a waste if you find you will not use it.