This site has a variety of matching activities for many different categories of vocabulary. You can match pictures to words, sounds to words, sounds to pictures, and more.
This site has a variety games to practice vocabulary and grammar.
This is a great online tool for finding synonyms, antonyms, and words in a sentence fast.
It even has pronunciation and rhyming words.
Multiple choice questions with explanations when you answer wrong - high level vocabulary that's good for SAT practice
Exercises for the Academic Word List
The AWL is a list of words that occur frequently in Academic English. This site has many fill-in the blank exercises – good for reading practice too.
This has excellent but difficult reading practice. Vocabulary from the Academic Word List is highlighted and there are fill-in the blank activities that follow each reading.
This site is for native English speakers preparing for standardized tests but you may find something interesting.