I consult the Merriam Webster's Collegiate Dictionary, eleventh edition, for matters of spelling and definition.
My primary style book for manuscript editing is The Chicago Manual of Style, sixteenth edition (CMS16). I also refer regularly to The Christian Writer's Manual of Style, updated and expanded, by Bob Hudson.
Depending on the requirements of the project, I may also use any of the following style books:
- SBL Handbook of Style, second edition
- The Associated Press Stylebook and Briefing on Media Law
- The Web Content Style Guide
- Your own house style guide, if you have one