The Online Writing Lab at Purdue University has TONS of great resources for common grammar and writing questions students have.
Teacher Tube is a site where teachers and students upload videos of class projects, lectures and other videos to aid learning. For example, you can search for videos of teachers demonstrating how to correct fragments or School House Rock videos about grammar.
The United States Army has created a site called "March 2 Sucess." Students over the age of 13 can use the site to help study for standardized tests like CRT, ACT or SAT. It also gives advice on applying for a job.