Technical Writing Textbook
The 20 Most Common
Errors in Writing
This site has an array of dictionaries to choose from.
Merriam-Webster Online Dictionary & Thesaurus
This site includes an audio pronunciation feature. Click on the red audio icon next to a bolded word to hear it pronounced.
An extensive, user-friendly resource on grammar. Includes information on grammar rules, instructors' margin comments; also provides answers to frequently asked questions and links to other writing resources.