Fullsail

As a teacher, you can create a free teacher account through which you can create student accounts. Diigo's student accounts require no email address, can be kept private, and can also be grouped so that students can share resources they find with each other. 

While observing my students using Diigo, I noticed that they were actually reading the site and highlighting the information they wanted to keep.  This was different from previous years where they just copied blindly.  In addition, they could easily return to where they left off the previous class.