Shmoop is sort of a Cliff’s Notes — but a whole lot better.
It has a literature and poetry section, but I’m less interested in those since I’m not convinced that using the “classics” in any kind of class — mainstream or ELL — is the best tool for teaching and learning. However, I like its History section. It’s probably only accessible to advanced English Language Learners, but teachers could certainly easily modify parts to create more usable materials. It also offers links to additional good resources.
I’ll be adding the link to the Teacher’s Page of my website under Social Studies Resources.