I tried
FreeMind and
XMind software. Both are free.
Though XMind could take a lot of time to load, I found it is easier to handle than FreeMind (TAB produces sub-topic in XMind, while INSERT produces siblings in FreeMind).
One big advantage of FreeMind over XMind is the ability to export it as JavaApplet and Flash. I hope XMind developers consider this.
I have been importing XMind to JPG file and loading on to my blogspot (
http://mind-mapped.blogspot.com/).
Further, both fail in online collaboration, though other online tools are available.
Anyway, the Mind Map is a cool tool - for taking notes, for remembering stuffs and for brainstorming new ideas.