It has an incredibly impressive collection of materials — on just about any topic imaginable — that are very accessible to English Language Learners. Over past few months they’ve even added audio support to much of their text resources, which made them even more accessible.
They just completely revamped the site, and now have hundreds of resources hosted by the site itself, slideshows, a much better internal search engine, and a bunch of other features.
You do have to register to use the site, but it’s free and easy to do so. You can register on behalf of an entire school, or on an individual basis.