I used Edmodo. This program will be really fun for my students. I may decide to have them respond to polls, post assignments, and share their thoughts about what we are learning. The kids will enjoy using it because it looks like facebook and so it's got a novelty factor that they will like. The program encourages a community feel for the students to share their thinking with others in class. I created an account for a teacher training, and I thought it really enhanced my learning.
http://sbisd.edmodo.com/withem You may not see much on the public profile as I have tried to keep things private for security purposes.
I also used Wallwisher for this post. http://wallwisher.com/wall/withem I think this would be a great activity for them to use during a technology station. They can respond to something we learned in class. I could use it as part of their observation grade, too.