The following are books, reports and online references that we find useful:

The Business Writer's Handbook: Seventh Edition
by Gerald Alred, Charles T. Brusaw and Walter E. Oliu
A useful desk reference organized alphabetically covering issues of form and usage.

Common Errors in English
by Paul Brians
http://www.wsu.edu/~brians/errors/errors.html
An online reference guide to the most common usage errors writers make, organized alphabetically. e.g. affect v. effect and their/there/they’re. We recommend bookmarking this site.

A Concise Guide to Technical Communication
by Laura J. Gurak and John M. Lannon
An introduction to the world of technical writing with special emphasis on digital forms.

Eats, Shoots & Leaves: The Zero Tolerance Approach to Punctuation
by Lynne Truss
A lively approach to learning the fine art of punctuation.

The Elements of Style, Fourth Edition
by William Strunk Jr. and E. B. White
The classic plain English handbook that never goes out of style.

Grammar Troublespots : A Guide for Student Writers
by Ann Raimes
An easy-to-use grammar reference for non-native speakers of English.

The Merriam Webster Online Dictionary
http://www.m-w.com
Need we say more? Bookmark this one too.

Writing: a Ticket to Work. . . Or a Ticket Out—A Survey of Business Leaders.
http://www.writingcommission.org/prod_downloads/writingcom/writing-ticket-to-work.pdf
The National Commission on Writing’s report based on their survey of 120 major American corporations. Nearly half of the companies surveyed provide writing training for their employees. The commission estimates that American businesses are spending approximately 3.1 billion dollars annually providing writing instruction for their employees.

Writing on the Job: A Norton Pocket Guide
by Margaret A. Mansfield and John C. Brereton
A good overview of the genres that writers encounter at work—from basic business letters and reports to press releases, newsletters and flyers.