Banished Words List
http://www.lssu.edu/banished
Every year a group of "word watchers" compiles a list of words that should be banned from the English language. This link goes to the current list. They have included a complete list of all the suggested words to be banned. Take a look to see which words you commonly use. Click the year to see not only that word, but the entire list for that year. You will also find lengthy explanations of these words and the reasons they are to be "banned". Look at the archives for previous year's entries.
English Through the Ages
http://www.bluerider.com/english/
OK, this might not be a site to learn about fragments or subject-verb agreement. This is a site to other sites with information on the history of our language. By studying the history of the English language, you can understand why we make "knife" plural by changing the spelling to "knives." Take some time to view the history of our language.
The American Heritage Book of English Usage
http://www.bartleby.com/64/
From their site: "With a detailed look at grammar, style, diction, word formation, gender, social groups and scientific forms, this valuable reference work is ideal for students, writers, academicians and anybody concerned about proper writing style."
The Elements of Style
http://www.bartleby.com/141
Truly one of the original guides of using style in your writing. While Originally published in 1918, the guide is still relevant and useful for students and educators. The rules are easy to understand and are to the point without being overwhelming. Take some time to "walk" through this wonderful guide. If you truly find it useful, you can find a copy at your local bookstore
Bartleby.com: Great Books Online
http://www.bartleby.com
An excellent source of reference books in the public domain. You can search for a particular subject or title. You can also browse popular titles by using the pull-down links along the right side of the page.
Heteronyms
http://www-personal.umich.edu/~cellis/heteronym.html
The problem with the English language is use of heteronyms in text. A heteronym is a word that has different meanings depending on the pronunciation. For example the word "read" can be pronounced as "reed" or "red" depending on its use as a past-tense or present-tense verb.
Spelling Test
http://www.sentex.net/~mmcadams/spelling.html
Admit it you miss the days of spelling tests in your reading or writing courses during your school days. Well, now you can take a spelling test to see how well you spell.
Commonly Misspelled Words
http://www.wsu.edu/~brians/errors/misspelled.html
Now that you have taken the spelling test (above link), it will be nice to have a list of commonly misspelled words.
"Saying" Errors
http://www.wsu.edu/~brians/errors/more.html
An extensive list of words and phrases commonly misused or misspoken.