Grokking is new to me--looks like a powerful search possiblities that allows a mindmap of related terminology. You can create a teacher account, specify difficulty level, create graphs and more. Looks very interesting.
Good blog on what teachers should be able to to with mobile learning for 21st Century learners. Has sensible links too to social bookmarking, audio and more.
Put away your EZ-graders, teachers, QuickGrade is the easiest grade calculator around! Use this tool to make grading stacks of tests a snap. Made with love and totally free to use!
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.