Great Source has a number of free student resources for writing on its website.
I like several slideshow tutorials in particular that are accessible to High-Intermediate and Advanced English Language Learners. They have ones for Persuasive Essay, Response to Literature, Research and others.
They would be nice supplementary resources for the WRITE Institute units we use at our school. As I’ve written before, I believe WRITE Institute lessons are the best ones I’ve seen for helping English Language Learners develop their writing skills — bar none.
I’ve placed links to the Tutorials under the appropriate sections on my English Themes For Intermediate/Advanced page.