insightin.com - vocabulary test
How big is your English vocabulary? Visit this site and take the vocabulary size test and find out! A native English speaker with a degree is able to understand about 20,000 words. For ESL learners, minimum of 10,000 words is necessary to score high on TOEFL, GRE and GMAT. This 50 multiple-choice question Vocabulary Test is designed to test vocabulary size between 1,000 and 10,000.
In addition to the vocabulary size test there are also lists of the 6000 most commonly used words in English and several other related sections.