The 21st Century Teacher is a new social network that intertwines nicely w/ Facebook and Twitter. This social network is brand new and slowly growing and is a nice alternative to other great teacher network such as Classroom 2.0 or Educator's PLN.
This network has a bunch of groups to join such as Instructional Technology Specialist to iPads in Education. Another nice feature is the community blog and the easy in which one can share and post documents. I highly recommend checking out 21st Century Educator by clicking here!!