How to Win Friends and Influence People : A classic, and still great! This book is old enough that it is available for free now. It has outlived it’s copyright.
http://www.drmardy.com : This looks like a website, but it is also available as a book. Useful for finding information to spice up your writing. 2500 quotations containing metaphors.
The 16-Word Sales Letter™: A proven method of writing multi-million-dollar copy faster than you ever thought possible : Evaldo Albuquerque’s book. That name may not mean anything to you, but Evaldo is not a native English speaker. And yet, even though English is not his first language, last year alone, he was able to sell over $80 million for Agora Financial. That’s so shocking that Bill Bonner, the founder of Agora said this “For years I’ve been asking myself, how can a guy whose native language is not even English be one of the best US copywriters in history?” A co-worker of mine was scared about her prospects to work as a writer because she’s not a native English speaker. That’s when I showed her Evaldo’s work.