The invisible bookshelf. Not as good value as the Argos shelves reviewed on the last show. The usp is that you can't see the shelf once you have put some books on it. My daughters each have one of these above their desks and they look cool:) You can get quite a big stack of books on them. Some DIY skills needed as you need to drill some holes in your wall.
They seem to be about £15 on Amazon at the moment, but I think I got mine for around £10, so shop around.