Tutor2u-Wisdomap (say that 10 x's fast) is an excellent site I just found out about from the equally impressive blog ZarcoEnglish. This is a great site for making mind-maps specifically designed for education.
Here is a quote straight from their site, "Tutor2u-Wisdomap is the only mind mapping software designed for education. Packed with useful features for in and out of the classroom, tutor2u-Wisdomap helps you to make beautiful mind maps and integrate engaging media items. You can use it to plan lessons, set and track mind map assignments for your students, create interactive mind map presentations. Your students can get the most from mind maps using the unique built in revision tools."
For more information on Tutor2u-Wisdomap click here.