Xmind - Xmind is a brainstorming and mind mapping application.
Idealist - Volunteer, work, and intern job search
MindMeister - Create, share and collaboratively work on mind maps with MindMeister, the leading online mind mapping software. Includes apps for iPhone, iPad and Android.
Idea Hunt - Solve specific challenges for your favorite products
Viima - Viima is the simple, yet incredibly powerful Agile Innovation Platform that helps you go from ideas to innovations – at the speed and scale of a true innovator.
Nugget - Find your perfect startup idea