I am totally hooked on Larry Ferlazzo's Websites Of The Day For Teaching ELL, ESL, & EFL blog and his Teacher Page. This guy is a non-stop search engine and comes up with 2-3 new English teaching sites per day.
As always, caveat emptor: you will need to check each site that sounds promising to see if it really matches your English learners' abilities and interests. Many, many sites on the Web look good for learning/teaching, but often are of simply too high a language level to be of much use to learners. Those that Larry recommends are no different. With over 7,000 sites noted, however, you will probably find many of use.