ESL Bee is a teacher-designed site to assist Intermediate and Advanced English Language Learners in writing academic essays.
There’s a lot of material there. For me, though, the gold mine is in the examples of student essays (for example, these persuasive essays). It’s not easy to find good, short, accessible, and well-written examples of different types of academic essays that can be used with English Language Learners as models, but you’ll find a wealth of them here.
The same site also has a number of good English practice quizzes.
I’ve placed the link on my website under Practice Writing. I’ve also added it to The Best Websites For K-12 Writing Instruction/Reinforcement.