Recently, I added support for Hypothesis to Pragmatically Cynical. This is a great free, open-to-use tool for use in adding annotations to web sites as you browse, either for your own private use or for more public sharing and discussion. On Pragmatically Cynical, any browser can access the capability now by highlighting some content and right clicking on the highlighted content. Users of Hypothesis can see and recall the context of the reference and annotation when you go back to use the reference at a later date, and see those annotated by others (provided they make the annotations public).
Another great part of Hypothesis is that it lets you work anywhere on the Internet via a Chrome plugin, even if the site doesn’t natively support it.