I've sent an email to the group pointing-out the two links to hundreds, if not thousands, of vocabulary sites that I've linked to my website. In case you missed the email, the links are:
Vocabulary Sites For Beginners and Early Intermediate
Vocabulary Sites For Intermediate and Advanced
I'd also like to highlight a few of my favorites.
Learning Vocabulary Can Be Fun has numerous games, including many with audio, which are fun and effective with my ESL students. Students don't learn the words in context of sentences, but you can't necessarily expect everything from one site.
The Language Guide is an extraordinary picture and audio dictionary that is organized well and covers the basics.
Basic Sight Words covers the most commonly used words in the English language. On particularly great element of this site is that words are taught in the context of sentences. You won't find this link in my Vocabulary sections, though. I have a completely separate category called Sight Words that has a zillion links about.....Sight Words.
Finally, I love a site called Willing to Try. It's hard to explain what it is. Try it out (be sure to have your pop-up block turned-off, though). I think you, and your students, will enjoy it.