Cambridge University Press has extraordinary online support activities for their ESL/EFL textbooks, and they’re freely available to anyone. Several of their sites are on The Best Listening Sites For English Language Learners.
Now they’ve just come-out with a site for adult learners (which I think would also be fine for high school students). It’s called the Ventures Arcade, and it’s really top-notch.
I’ve placed the link on my website under Favorite Sites.