I use Diigo to bookmark in the "cloud" and organize websites I come across as I read, follow people on Twitter, or read blogs. Organization is done by tagging - -adding descriptive workds to bookmarks. Many of the links to materials in our course are my bookmarks tagged by a particular topic. As you can see, bookmarks can easily be shared with others.
You can also set up a RSS feed (I've done this on our wiki webpages) so that those pages are updated anytime I add a new bookmark to a tag. This is also how the "who's writing" widget works on the front page of our course website.
Diigo allows you to install a tool in your browser so that bookmarking is easily done with just a few clicks.
I can also connect my Twitter and Diigo accounts so that my favorite Tweets are saved to Diigo.
And finally, Diigo also allows me to connect with my blog by setting up a tag unique to the blog. If I read an article that I want to post to my blog, I tag it with that distinctive tag and a short time later, a link to my article along with any text i've highlighted or comments I've made are publised on the blog.
I'd recommend this article on using Diigo in the classroom as an overview.