Grammar Explanations and Quizzes http://grammar.ccc.commnet.edu/grammar/
The OWL at Purdue. For all your writing questions. http://owl.english.purdue.edu/owl/resource/747/01/
Diana Hacker - Documenting Sources http://www.dianahacker.com/resdoc/p04_c08_s1.html
Merriam-Webster Dictionary http://www.merriam-webster.com/