I am a big fan of diigo (social bookmarking), which is not typically used in schools and I think it should be used much more. Here's a sensible approach to using with students.
ICT Magic was selected as the best educational blog for 2011. I particularly like this page (which has links to lots of resources) from clip art to virtual destops.
Edumodo has lots of potential for teachers and students; you can control who is part of the group and you can monitor, two important considerations with social media and students.
Naiku functions like an online clicker. Ask a question and students respond via enabled device (tablet, iPad, smartphone, computer). Free for teachers. Looks interesting