Several of these tools will be useful. Two of them would specifically help in an area where I have found challenges.
First of all Diigo would help me, in that I am constantly pulling up resources to help emphasize concepts I am teaching, but they get lost between classes. Diigo would help me keep track of them more efficiently. Also, Diigo would help me to focus my students' research. For instance I would like to assign different groups of students to research different Elements of Art. By bookmarking my preferred resources in Diigo, I can insure that they will be finding the right definitions and keep them focused on their search.
Students can use Google Docs to report their findings on their assigned Element and share them so that all students receive the information they need. Edmodo could also be used for the same purpose. The benefit of Edmodo is that I could create a group for each class and save the findings for that particular class.