Padlet
Here is an example of a Padlet: http://padlet.com/kdfrench/socialmedia Note that this Padlet does not require login, but there are a variety of privacy options for viewing, editing, and moderating comments.
There is a free version, but a paid version allows for more customization and control.
To get started with Padlet, go to: http://jn.padlet.com/category/38-getting-started