elegant communication

These days, most reference materials can be accessed online; even Chicago has a pay website if you don't want to deal with the hardcover version.

• American Writers and Artists, Inc. for all things related to direct marketing.
  
  
• Writers Digest for just about every imaginable reference book on writing.
  
  
• Dictionary.com for online dictionaries and thesarus.
  
  
• The Chicago Manual of Style even has an online version now. (I still get the hard copy. :))

There are cetainly a LOT more reference books on my shelf, but here's the basics. :)

Writer's Digest magazine, books, and courses
Writer's Digest helped me early on as a writer before I started doing it "professionally," and it can help you also! For example, back in the day, the screenwriter for Babylon 5 had a regular column and he talked about how the storyline took place over five seasons. Writer's Digest is also where I learned that the Klingon language was created specifically without a form of the verb "to be" (apparently a pet peeve of the writer as well as one of mine!) — until Warf was given that scene with the "To be or not to be..." soliloquy. :)

Write Tight: How to keep your prose sharp, focused, and concise by William Brohaugh
This book will teach you how to write in active voice and make your verbs do the work instead of adjectives and adverbs.

Elements of Style by Strunk & White
Yes, that's EB White of Charlott'es Web. This is the classic grammar book. Short. Sweet. And easy.

On Writing Well by William Zissner
A classic on writing non-fiction.

Chicago Manual of Style, 16th Edition
If you are not familiar with Chicago, I highly recommend. This is the style guide used by most book publishers, and most corporate styles are also based on it. It contains a wealth of informaton on publishing, writing, ediitng, and structure.

Microsoft Manual of Style for Technical Publications, 3rd Edition
The 4th edition is due out in November 2011.

American Heritage Dictionary
There are several dictionary websites that also use it. This is the only dictionary that provides usage information, such as the on-going argument over -ize verbs.