Bubbl.us is a free online tool that can help students with the brainstorming at the beginning of the research process.
No sign-up is required for using and printing ideas. This is a quick and easy tool for kids who are visual learners. This is also a nice piece to come back to (if you've signed in and saved) for organization purposes.
This article features bubbl.us and many other mind-mapping tools that may help your students generate and work to connect ideas.