This one almost goes without saying. What writer wouldn't want a copy of the Writers & Artists Yearbook? Unless, like me, you'd prefer the Children's Writers and Artists Yearbook.
Overflowing with information on the industry, the Writers and Artists Yearbook is a bible for most writers. Not only does it contain up to date information on industry professionals and organisations, but it also includes a number of wonderfully informative, helpful and encouraging articles from writers and agents etc.