Writing Rescue Guide for Students: Excellent collection of resources. 
Avoiding plagiarism: Clearly explains the difference between legitimate paraphrasing and copying that could get you in trouble. 
Guide to Citing Internet Sources: Lot of good information about how to evaluate Internet sources and how to cite them. 
Plagiarism on Campus: Good explanation plus tools you can use to proactively check your work. 
Writing Progress: This free academic writing assistance Web site provides advice and writing tips from experts.
William Strunk's The Elements of Style (1918 edition, online): Despite its age, this short classic will do more to improve your writing style than any newer or longer book.
Online Resources for Writers: A good collection of links to many of the major online writing resources.
Resource Guide to Writing Basics: A useful guide to basic writing skills. 
Writing Guide: A useful general guide to writing papers, from Henson College.
Grammar Education Resource Guide: a lot of in-depth information about grammar resources.
Guide to Grammar and Writing: Excellent and thorough discussion of grammar and composition, includes tutorials, links, and FAQs.
Style Guide Resources: A detailed list of style guide resources for the MLA, APA, Chicago, and CSE styles.
Online College Writing and Training Guide: A well-organized set of resources designed to help you improve your writing skill. 
Home Page of William Stallings