One of my favorite Nings is EFL Classroom 2.0 It is designed for English Teacher's and Learner's. I enjoy it because it sparks so many ideas. I discovered this site when I was looking for review games to use in my classroom. I discovered BAAM games, they are power point games. I took the templates and used my own questions and answers. My kids love the game.
I am also a big fan of random generators. David Deubel created the EFL Classroom 2.0 Ning Network. He is an incredible creative educator. Recently he created a random blog generator. He has put over 100 blogs into the generator. Each time you click on the generator you read a new blog. Try it out.