I have written about Shmoop in the past (see my article: “Highlight of Product at the AP Conference Shmoop“). If you are unfamiliar with Shmoop, think of them as an all inclusive website for study-guides, lesson plans, student and teacher resources, and sample standardized test repository (just to name a few). While Shmoop offers a wide variety of paid resources (inexpensive and well worth the investment it in my opinion), they also have ample free resources for both educators and students.
If you are looking for a great review of material, check out their “Free Learning Guides” that cover a myriad of topics from literature to mathematics. They also have a great repository of learning videos under their “Shmoopsterpiece Theater.”
If you are looking to provide guidance to students preparing to leave High School, try the section on “Shmoop Careers,” where students can take a brief aptitude and interest test and receive guidance, or “College 101,” which can help students to select a college or university that will meet their needs, complete a successful application, and get funding.
New material is added regularly, so this is a site to bookmark!