A few established and widely used style guides include The Chicago Manual of Style (US), the Associated Press Stylebook (US), The Oxford Style Manual (UK), CP Stylebook (Canada), and many, many others. However, an organization may have an internal house style that includes issues not covered in most general-use style guides or that vary from these established guidelines.
In addition to some of the major style guides, certain fields have their own very specific style guides such as AMA (American Medical Association) or Bluebook (legal profession).
Writers and designers may be required to use spelling, formatting, and other style issues that vary from one client to the next depending on the style guide preferred by the customer.
Buy a Style GuideThe Elements of Style (general public classic)
The Chicago Manual of Style
Pocket Guide to the Chicago Manual of Style
MLA Style Manual and Guide to Scholarly Publishing
A Manual for Writers of Research Papers, Theses, and Dissertations (Turabian)
New York Public Library Writer's Guide to Style and Usage
The Business Style Handbook
Business Grammar, Style & Usage
The ACS Style Guide (scientific)
The Redbook (legal)
The Bluebook of Grammar and Punctuation
AMA Manual of Style (medical)
Writing the Research Paper (MLA & APA Styles)