http://thinkature.com/ (There must be also some software to do this, but I don't know any. You could try and look for something like 'whiteboard software')

http://www.mindmeister.com/Basic version is free, it is especially good for creating maps as a group.

Free open source, quite basic but good for classic mind mapping http://freemind.sourceforge.net/wiki/index.php/Main_Page

from the inventor of mind mapping, visually the best one I think. You can have a free trial but the programme is kind of expensive http://www.imindmap.com/

Mindmanager is the most commonly used one, I guess because it was the first mind mapping software on the market. http://www.mindjet.com/products/overview.aspx?google_be=mindmanager

personal brain