I brainstorm is a free App for the Ipad and IPhone from Universal Mind which claims to make it easier to capture and share brainstorming sessions.
The App acts as a virtual whiteboard where up to five users can collaborate on brainstorming sessions and send their notes from the IPhone to the Ipad. It has a Wallwisher kind of feel to it with the use of sticky notes but also allows users to draw and write onto the canvas.
The App looks very promising but did get mixed reviews from Macworld. The reviewer complained of a few limitations such as the inability to modify emailed or saved sessions or to change the size of the felt tip pen or sticky notes, making it hard to see everything clearly on the Ipad. I think that since the Ipad can be connected to a larger display with mirroring, the this problem would not be a major issue. It looks like it could be a great tool for teachers to use in the classroom to brainstorm ideas with students by projecting everything on a large display.
Given that the App is free, there is certainly no harm in downloading it and testing it for yourself. Please do provide feedback if you have tried the app yourself.