TED is chock full of amazing content from the world of thinking, making, creating, innovating, etc.
Most folks know about it by now, so why include it? TED-Ed for one, but for two, it is transformative for enabling customized delivery of the content with piles of UDL features. It's just awesome.
Customized news feed that is more visual than text.
I cannot stand RSS feeds -- this, however, makes me crave more news. Similar to Flipboard, but less ornery on my classic Android Incredible v1.0
Excellent mechanics, grammar, usage, spelling (MUGS) site that allows you to work at your own pace and customize some of the content of the examples with sports, celebrities, music, etc.
Great place to work at your own PACE!
This program (some parts of which are free) allows you to customize the math standards based activities you can assign kids. It will quiz them and assign intervention modules if needed by topic. You can track all of the kids all of the time.
My preferred means of collecting and sharing links.
Fully integrates with Delicious -- which had been at the top of my list until their new stacking system which I find . . . well . . . gross.
LOADS of other functionality around groups, discussions, annotations, note taking, sharing -- really well designed and gentle learning curve.
Think of this as an educational Pinterest. You can create a "learning board" where you collect almost ANYTHING from the web you'd like on a topic. People can browse through your boards (or you on theirs) and see embedded video, google docs, forms, other boards. Combines with LOTS of services, Edmodo, Quizlet, Prezi. You can like, comment, share, and track your progress.