I've recently learned about Diigo, a social bookmarking tool with some cool features that include highlighting pages and pasting sticky notes. These get saved to your Diigo account so that no matter what computer or device you're using, once you login to Diigo your bookmarks, highlights, and comments are there. Even better is the ease with which you can share web pages with others, Diigo users and non-users alike. In addition to linking to your Facebook, Twitter, or Google+ account, you can also send a simple URL to folks like this: http://diigo.com/0so2w
If you're a teacher, Diigo is offering a free upgrade to an educator account that allows you to form groups and "enroll" students with their own accounts. Anything that any of the students bookmarks is then shared with the entire group. This is a great way to tap into students' inclination toward social media.
And, to top it off, as a Diigo Educator, you'll get a cool badge to put on your site or blog!!