Here you will find links to websites that teach and test English vocabulary.
There are other pages on this part of the site that deal with specific types of vocabulary: academic, idioms and phrasal verbs.
The ESL portals page has links to websites containing vocabulary sections.
Match the words and pictures - a simple quiz for beginners.
The Internet Picture Dictionary - basic vocabulary with various quizzes.
Basic English picture wordlist from Wikipedia. Each picture links to information about that word.
Another Simple English Wikipedia page. Each entry on the starting page links to examples, grammar information and an audio file pronouncing the clicked word.
Lots of interesting stuff about vocabulary, including various online tests.
There are hundreds of quizzes of various types linked to on the vocabulary index of this site.