A.nnotate is the newest addition to The Best Applications For Annotating Websites.  You can read more at that list about why I feel a tool like this is so critical while working with students — I’m still amazed that there are so few easy-to-use web applications out there that let you easily make these kinds of virtual “post-it” notes.

Instead of describing A.nnotate in detail here, though, I’m going to suggest you read a very thorough description of it — with screenshots — at The Make Use Of blog.