Writer's Handbook:  Grammar and Style
Information on various grammar rules and writing styles.  Includes lists of parts of speech.  Maintained by The University of Wisconsin-Madison Writing Center.

Guide to Grammar and Writing
Maintained by Capital Community College, this site offers samples of business letters, resumes, research papers, and more.  Also provides grammar tutorials and over 150 interactive grammar quizzes.

Guide to Writing a Basic Essay

OWL
Purdue's Online Writing Lab covers a multitude of writing strategies.