DICTIONARY, ENCYCLOPEDIA AND THRESAURUS
The Free Dictionary
(Listen and read the phonemes e.g. Police)
Besonders zu beachten sind Wörter, die im Deutschen eine ähnlich
lautende Entsprechung haben: 
Compare-Vergleichen (PDF, 0.22 MB)
GUIDE TO ENGLISH PHONETIC SYMBOLS
Phonemic chart (British council)
Phonemic chart - Adobe flash (British council)
Phonetic symbols chart
Phonemic character keyboard
GRAMMAR
Skillwise (Practical literacy skills for adults)
GRAMMAR AND VOCABULARY
Flash Quizzes for English Study
Improve your vocabulary
IDIOMS
Self-Study Idiom Quizzes
ENGLISH AS SECOND LANGUAGE
Quizzes, tests, exercises and puzzles to help you learn English as a Second Language (ESL)
This project of The Internet TESL Journal (iteslj.org) has thousands of contributions by many teachers.
Activities for ESL Students