ROBERT LESLIE FIELDING
Be kind to everyone you meet.
You may never see them again.

Let's try this link first - probably more use to teachers than students.

http://www.lextutor.ca/

And a quiz builder

http://www.lextutor.ca/concordancers/multi/

And this Vocabulary Profiler

http://www.lextutor.ca/vp/eng/

Vocabulary exercises for students

http://www.angelfire.com/wi3/englishcorner/vocabulary/vocabulary.html#colls