The Chicago Manual of Style

This style guide is especially popular with academics, technical organizations, and book publishers.

The Associated Press Stylebook

The AP Stylebook works well for organizations that publish content similar to newspapers and magazines.

Gregg Reference Manual

This is considered a business writer's style manual and is probably the easiest of the three to use.

Specialty Guides

These style guides will be helpful to you if you work in these specific fields.

American Medical Association Manual of Style

MLA Handbook for Writers of Research Papers

Publication Manual of the American Psychological Association

Microsoft Manual of Style for Technical Publications

Scientific Style and Format: The Council of Biology Editors Manual for Authors, Editors, and Publishers

Wired Style: Principles of English Usage in the Digital Age