The resource I found most useful, interesting and appealing was the CommonLit site.  This is a fantastic resource that can easily be translated directly into classroom lessons.  It's got a clear searchable database to find lessons based on grade level, content type, Lexile levels, standards, genres and a number of other useful criteria.  Not only does it have an extremely wide variety of literary and informational texts, they include lessons, learning activities, related materials and differentiated learning strategies.  

I did a search for material aimed at grades 6-12 since those will be the grades I'll eventually be licensed to teach, leaving all other criteria blank.  All kinds of interesting and varied results came up, from short stories to news stories, science fiction, poetry, skill lessons, and various focused informational texts.  I took a look at a fascinating informational text on the psychology of herd behavior and found the following:

The first thing you notice is that there are number of accommodations for differentiated learning.  You can adjust the font size for people with visual difficulties such as the Old Man Eyes I'm forced to see the world through.  There's also a read aloud feature as well as a translate function for ELL students.  The text has a guided reading mode that asks comprehension questions as students read, along with assessment and discussion questions.  There are tabs that bring you to a parent guide about the lesson, and also a "Related Media" and teacher guide tab that are both only accessible if you have an account (which I may eventually get given the value of this resource).  One of the best features is the "Paired Texts" tab, which brought me a slew of other equally fascinating lessons having to do with psychological phenomena or conformist behavior or group think or what-have-you, along with suggestions on how to integrate each lesson with the one on herd behavior.  

I was genuinely impressed by the content available on this site, the comprehensive and integrated nature of the lessons, and the ease and clarity of the search engine.  Some of these education-oriented sites have search engines that result in a confusing mish-mash of lesson plans, tests, templates and other materials that don't have any kind of uniformity or consistent formatting.  This one is crystal clear and also doesn't give you an ugly kaleidoscope of pop up ads to slow down your browser and mangle your viewing experience.  These guys must have a pretty effective nonprofit organization behind them because I didn't see any ads at all on the site, which is a welcome difference from many of the other web-based educational resources I've seen.

I'll at the very least be bookmarking this site for future reference, and may well sign up for an account and use it while developing my own lessons.