For writers/artists/journalists this book is a must-have. It's packed to the rafters with useful info about publishers, agents, magazines, newspapers, greeting card manufacturers...all detailing what work they accept, how to send it, who to send it to. It even has fascinating notes from authors giving their views on the cruel world of writing (!), it covers legal issues such as copyright and also has info on financial aspects of writing (e.g. tax, self-employment etc).
An invaluable reference book if you're serious about becoming a professional writer/artist and hoping to make a bit of cash out of your talents.
It's an industry where research and preparation count for a lot, so in understanding your potential market you're instantly improving your chances of success.