I like
Wallwisher because it works so much like the "post-it" brainstorming exercise so many of us use with staff or students. All you have to do is create a wall, and then send out the link to those who will be collaborating with you. Users can re-arrange the notes, and group them according to themes or sub-topics or what-have-you. One great spin-off is that you have a more permanent record of your brainstorming, instead of a poster with loose notes that tend to fall off and get lost. With a digital projector and a laptop, it makes an engaging way to record group thinking.
