This is probably one of my favorite sites/discoveries thus far in my computers in ed class. It is a social networking site called Ning and it is free! It was simple to get started and really simple to personalize.
But what can a teacher use this for? It can be made into an interactive teaching site for the classroom, a place where students can interact with the teacher (great for sick days) while creating a place that is a safer than a facebook or myspace. Also it is a great site that parents can easily be updated with! I encourage all teachers to look into this site :)
Here is the link in case you want to preview a sample