Buy this book.

I came across it today. I have bought the Writers/Artists yearboook for the last few years, it's a great book, very informative, full of great advice and addresses to every agent and publisher for any kind of writer and illustrator.
Although it does give advice and addresses for screenwriting it is definately only for writers. But the Filmmakers Yearbook gives addresses for production companies, agents, techicians, financial bakers and much much more.
It is probably one of the most useful and practical film books I have ever come across.