Visual Thesaurus
This unique multimedia thesaurus gives you a visual display of similar words to any word you enter. You can also choose to display words with other relationships to your selected word.
Intended Audience: General Reading Level: N/A Teacher Section: No Searchable: No

Merriam-Webster
Not sure how to pronounce a word? This site from Merriam-Webster features a dictionary that gives you definitions and audio pronunciations of words! Want more? How about a thesaurus, word games, a word of the day feature. and audio files and transcripts of the radio show Word to the Wise that airs on Public Radio and gives a daily glimpse into the world of words and language.
Intended Audience: General Reading Level: Middle School Teacher Section: No Searchable: Yes

California Virtual High School Test Prep
Practice for the SAT, ACT or brush up on your vocabulary skills. Online practice questions provide guidance when you get an answer wrong and explanations when you get an answer right. You will have to register, but it is free!
Intended Audience: Students Reading Level: High School Teacher Section: No Searchable: No

Grammar and Vocabulary Games
Check out these online grammar and vocabulary games from FunBrain. You can try your hand at Grammar Gorilla, try your luck with Spellaroo, or build your own Wacky Tale.
Intended Audience: Students Reading Level: Elementary Teacher Section: No Searchable: No

Chiasmus
This web site is devoted to the literary and rhetorical device known as chiasmus. Chiasmus is the the reversal of words in parallel expressions. For example, the phrase "Quitters never win and winners never quit." You can learn about the different types of chiasmus; read quotes from some masters of chiasmus like Oscar Wilde, Winston Churchill, and William Shakespeare; test your skill with a chiastic Quiz Show; or look at examples of chiasmus in the New Yorker and the Boston Globe.
Intended Audience: General Reading Level: High School Teacher Section: No Searchable: Yes

Glossarist
Looking for a glossary of nautical terms, how about a geometry glossary? Maybe you are looking for art terms. This site has catalogues and provided links to glossaries on the web.
Intended Audience: General Reading Level: N/A Teacher Section: No Searchable: Yes

Ask Oxford
Do you know what exauctorate means? How about trammel? If you like words, this site from the Oxford Dictionaries will provide you with games, puzzles, history, and usage tips!
Intended Audience: General Reading Level: High School Teacher Section: No Searchable: Yes

CNN Newsroom and Worldview ESL Web Exercises
This site from Brigham Young University-Hawaii features weekly interactive grammar and vocabulary exercises featuring copy from CNN news programs. The stories have words removed and students select the correct word or phrase to fill in the blank.
Intended Audience: General Reading Level: Middle/High School Teacher Section: No Searchable: No

Common Errors in English
Do you pronounce Nevada correctly? Do you know when to use predominate and when to use predominant? This site from Paul Brians, Professor of English at Washington State University has an extensive alpha list of common errors in English usage.
Intended Audience: General Reading Level: Middle/High School Teacher Section: No Searchable: No

Idiom Site
Elvis has left the building, catch-22, hold your horses. Learn the meaning and origins of these and other idioms at this site.
Intended Audience: General Reading Level: High School Teacher Section: No Searchable: No

American Slanguages
Can't tell your frappe from your quahogs ? This site features regional "slanguage" from the United States. You'll also be chuffed with the brill guides to language around the world.
Intended Audience: General Reading Level: Middle School Teacher Section: No Searchable: Yes

The Anagram Server
What do A RAG MAN, A NAG ARM, and MANA RAG all have in common, they are all anagrams for anagram. All you need to do at this site is type in a word and you'll get a list of anagrams.
Intended Audience: General Reading Level: Middle School Teacher Section: No Searchable: No