Vocabulary builders
Wordly Wise 3000 – Learn more than 3000 advanced words (good for SAT).
The General Service List – The most common 2284 English words.
Spelling Through Morphographs by Robert Dixon and Seigfried Engelmann. Designed as a one-year supplement to an English class for students who are already familiar with English. Teaches the prefixes, roots, and suffixes that make up English words, and encourages students to play with combining them to make valid words. Teaches spelling and vocabulary, plus a bit of grammar.
Word of The Hour – A tool that features one basic English language vocabulary word every hour with an active community on Reddit. For more advanced vocabulary words, see FunWithWords.
Word Menu by Stephen Glazier; A unique dictionary that is organized by subject