Bird Brain Science -- helpful intro video, two-month free trial, articles leveled for differentiation
Newsela -- current events in all content areas; various reading levels for all articles; built-in quizzes and customized prompts. Free accounts.
SmithsonianTweenTribune -- high interest articles, all content areas. Levels readings; lesson plans, quizzes. Free account.
Gale InfoTrack Junior Edition -- content-rich databases of articles and multimedia. Once you type in your search term, you can narrow results by lexile level using left-hand navigation. If a log in is required (when using off campus), type "student" (or you could use your public library card ID).