The Blue Book of Grammar and Punctuation
Jane Straus' reference guide and workbook
The Chicago Manual of Style
A publication of the University of Chicago Press
Common Errors in English
By Paul Brians. Simple, entertaining explanations of common errors in English
English-Zone.Com
The BEST English-Learner's site on the 'Net!
Guide to Grammar and Style
By Jack Lynch
Sharp Points
Bill Walsh's "vociferous rants" on matters of style
Silva Rhetoricae: The Forest of Rhetoric
A guide to the terms of classical and renaissance rhetoric. By Dr. Gideon Burton of Brigham Young University
The Vocabula Review
A society is generally as lax as its language.