Make the most of Open Educational Resources
Engage NY (the site that the state of New York uses):
CK-12 (has downloadable worksheets, as well as computer-adaptive practice): http://www.ck12.org/student/
Amazon Inspire: https://www.amazoninspire.com/home
Illinois DOE Open Education Resources: http://ioer.ilsharedlearning.org
OER Commons - Create, share and discover Common Core-aligned OER.
Connexions - OpenStax Connexions is an online community where you can view, collect, and share free educational materials and organize them into personal collections.
Curriki - Quality, free open educational resources for teachers, parents, and students.
Project Gutenberg - Thousands of free e-books in the public domain.
K-12 Tech Tools - A huge online database of tech tools for K-12 education.
School Forge - Free open source software for schools.
Creative Commons - Creative Commons develops, supports, and stewards legal and technical infrastructure that maximizes digital creativity, sharing, and innovation.
Utah's Open Textbook Project - A robust learning network and curated quality open educational resources for teachers.