For Math and English, check out Achieve The Core—
Free, vetted, adding more material everyday. This website is full of free content designed to help educators understand and implement the Common Core State Standards. It includes practical tools designed to help students and teachers see their hard work deliver results. achievethecore.org was created in the spirit of collaboration. Please steal these tools and share them with others.
Take a tour of this free service. Match text to grade level or lexile. Even contains full units on novels. Applies to all subject areas.
Current event articles that you can adjust according to Lexile. Sign up for the free version to download articles. Paid service is pricey but has nice features.
Peer reviewed, open source, free writing “textbook”
Note: Most of the subject areas have a link to a Pearltree on the left. This is full of all kinds of resources: content, instructional, and technology.