Boggle is a longtime favorite of ESL teachers and students alike. Another online version has been created called Boggle ClusCrive that’s very easy and accessible to English Language Learners.
You can register to play, or play immediately without signing-up.
I’ve placed the link on my Intermediate English page under Word and Video Games.
(I forgot to mention that you want to click the flag at the top of the page in order to play in English)