This Companion Website for Simon and Schuster Handbook for Writers, 8/e, from Prentice Hall is a convenient environment to practice and master composition skills. It includes exercises for basic grammar, research, mechanics and spelling to name a few. This site offers more than 1000 exercises on over 100 topics, as well as additional study tools.
Mechanics and Spelling
Resources for Writing
Research and Documentation Tutorial
Understanding Plagiarism Tutorial