Here are some more websites you might find useful:
Library of Congress - Historical archives & primary sources.
Culturegrams - detailed info about countries and US states
Pro-Con - the pros and cons of controversial issues
Online Writing Lab - advice on grammar, formatting, MLA, etc.
Issues Researcher - articles about controversial modern issues
Common Lit - passages to supplement reading of core texts
Duolingo - language-learning website
American Scientist - award-winning science magazine
Human BioDigital - 3-D models of the human body
Smithsonian - education and research complex
Pixabay - catalog of free-to-use images and photographs
National Geographic - articles related to science, geography, and history.
Desmos - graphing website.