Quicklinkr lets you very easily collect websites, images, videos, etc — without requiring registration. They are shown with screenshots, and you can put them into “folders.”
It appears you have to register if you want to come back to edit it, or to leave a comment about one of the saved links (registration is quick and easy). Unfortunately, that comment feature appears the only way you can add a text description to any link you save. There might be another way, but I didn’t see it.
I think it has a lot of uses but, for now, I’m just adding it to two lists:
The Best Social Bookmarking Applications For English Language Learners & Other Students