Common Errors in English Usage
A list of each error with a brief explanation of what is correct
Visual Dictionary Online from Merriam-Webster
The American Heritage Guide to Contemporary Usage and Style
Ebook. Read online. (Subscription resource. Log-in required for off-campus access). An authoritative survey of English usage, grammar, and style, offers guidance on almost any writing problem imaginable. Arranged in a single, easy-to-use A-Z list, the guide's entries include examples and quotations that show correct and incorrect usage.