Learn English feel Good (Vocabulary Page)
Lots of online vocabulary quizzes.

All

English Club (Vocabulary Page)
Excellent website with explanations and activities on every aspect of English learning and teaching (grammar, vocabulary, listening, business English, test taking, reading, pronunciation, etc.).

Activities for ESL Students
Mostly grammar and vocabulary. Lots of good quizzes and games sorted by level. Do the easy ones and work your way up!

Beginner to Advanced

The Teacher
Award-winning video series from the BBC designed to make learning English idioms fun. Each unit has a video you can watch and download to your computer.

Low intermediate to Advanced

False Friends (faux Amis) in English
A list of French and English words that look similar but have different meanings. Example sentences are also provided.

Intermediate to Advanced

Faux Amis en Anglais
More words that look the same but mean different things in French and English.

Intermediate to Advanced

Merriam-Webster
Excellent online English dictionary. Includes audio for proper pronunciation, thesaurus, crosswords, podcasts, and a whole variety of special features.

Be sure to check out Merriam’s Learner’s Dictionary as well.
http://www.learnersdictionary.com/index.html

Low Intermediate to Advanced

Free Dictionaries Project
This page gives access to a variety of dictionaries (multilingual, bilingual, unilingual, picture, specialty, thesaurus, etc.). Very complete.

Lexilogos
Another universal super-dictionary. Especially good for French-speaking learners of English.