Merriam-Webster's Vocabulary Builder
Newly expanded and thoroughly revised edition especially designed to improve language skills!
Usage and Style References
Merriam-Webster's Dictionary of English Usage
A critically acclaimed guide to English usage.
Merriam-Webster's Pocket Guide to English Usage
Quick answers to common usage problems.
Merriam-Webster's Guide to Punctuation and Style, Second Edition
Quick answers to questions about punctuation, capitalization, plurals, and quotations.