If you read a lot of books then Readitswapit.co.uk could save you a small fortune.
Usually once you've finished reading a book it more often than not gathers dust on a bookshelf. The sell on price for second hand books is pretty poor which is why a lot of people donate them to charity shops.
But Readitswapit.co.uk allows you to swap books you've read for ones you haven't. You simply find a book on the site that you like, you ask the current owner to swap, the ReadItSwapIt member chooses a book of yours and you then exchange.
So sign up, read, swap and save money (apparently even the most leisurely reader can save around £100 a year)!